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SCI 160 - Week 3
• John’s Back (hi!)
• Chapters 8-12
– DNA
– Gene expression and regulation
– How cells reproduce
– Patterns of Inheritance
– Biotechnology
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Chapter 8
• DNA: The Molecule of Heredity
• The Key to Life
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8.1 What Are Genes Made
of?
• Responsible for the traits we see in people
• Genetic differences (p. 114), minor and
major
• Early 1900’s discovered genes are part of
the chromosomes found in the nucleus of
every eukaryotic cell
• Then in the mid 1900’s it was further
narrowed down – they are made up of
deoxyribonucleic acid or DNA
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What Is the Structure of DNA?
• That was a good discovery, but how are
traits inherited? What is happening?
• What’s it made of? More chemistry…
• (Note – these are the most important
concepts in biology!!!)
• Each nucleotide is made up of a (1)
phosphate group, (2) a sugar (deoxyribose)
(3) one of 4 possible nitrogen containing
bases…
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Parts is parts…
• DNA Is Composed of Four Different
Subunits (nucleotides)
• (based on the nitrogen containing
bases)
– Thymine and adenine (p. 114) (T and A)
– Cytosine and guanine (p. 114) (C and G)
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T
phosphate
base = thymine
sugar
C
phosphate
base = cytosine
sugar
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A
phosphate
sugar
base = adenine
G
phosphate
sugar
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base = guanine
What Is the Structure of DNA?
• DNA is the molecule of inheritance for
all living things from bacteria to people.
• the phosphate group of one nucleotide
bonds to the sugar of the next…etc.
• A DNA Molecule Contains Two
Nucleotide Strands
– Figure 8.2 The Watson-Crick model of
DNA structure (p. 115)
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A
T
T
C
G
G
C
C
C
G
G
A
A
T
T
C
G
A
T
T
T
A
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A
A
Have a backbone
• Down the strands, the structure is held
by the sugar and phosphate molecules
connecting
• This is the sugar-phosphate backbone
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A
C
G
A
T
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T
A
T
What Is the Structure of DNA?
• Hydrogen Bonds Hold the Two DNA
Strands Together in a Double Helix
• It is the bases that connect via
hydrogen bonds.
• The strands are oriented in opposite
directions (like traffic on a two-way
road)
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Picky partners
• But the bases only like certain other bases
to join with (molecular/atomic bond rules –
too deep for this course)
• These are complementary base pairs\
• A only likes T, T only likes A
• G only likes C, C only likes G
• So if you have A-T-T-C-C-A-G-G-C-T
• then the other strand MUST BE
T-A-A-G-G-T-C-C-G-A
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T
C
A
G
G
C
C
G
A
T
C
G
A
T
T
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A
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How was it discovered?
• The discovery of DNA (p. 116)
• Early 1950’s – knew DNA did it somehow
• Watson and Crik broke the code (ahead of
the leading chemist of the day: Linus
Pauling, and two x-ray imaging scientists
Franklin and Wilkins)
• They got to see the x-ray images and solved
the double helix nature (and the information
coded in it).
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How Does DNA Encode
Information?
• How does the strand determine hair, feather, eye, skin,
colors? Sizes of organisms and components. Everything?!
• It is the sequence of the bases (4 to choose from).
• Our whole language is based on 26 letters (and a ‘squiggly’
for WalMart) and we can make a lot of words!
• Hawaiians only had 12 letters
• Computers only use 1 and 0!
• 10 nucleotides can contain a million base sequences
• A bacteria contains millions, humans contain billions of
nucleotides
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How Is DNA Copied?
• Why Does DNA Need to Be Copied?
– To create more of itself…children.
– To grow the organism
– To repair damage (grow replacement
tissue)
– Almost all the cells in your body have the
same genetic structure as the egg that was
your first cell.
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Xerox?
• DNA Is Copied Before Cell Division
– Called DNA replication
• DNA Replication Produces Two DNA
• Double Helixes, Each with One
Original Strand and One New Strand
– Basic features of DNA replication (p. 117)
– DNA replication (p. 118)
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Copies?
• Remember, each base only likes one
other base
• If one free set of ends looks like ATG,
then the only thing that will build upon it
is TAC
• (Be able to do this yourself).
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free nucleotides
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One DNA
double helix.
DNA replication
Two identical DNA
double helixes, each
with one parental
strand (blue) and one
new strand (pink).
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How Well Is DNA Copied?
• Proofreading Produces Almost Error-Free
Replication of DNA
– If no mistakes are made, then you have exact
copies of the original DNA strand
– 1 in 10,000 matches are mistakes, but get
corrected by ‘proofreading’ enzymes
– Completed DNA strands contain mistakes in only
1 in 1,000,000,000 pairs.
• Mistakes Do Happen
– Called mutations
– Chemicals, UV light, radiation. (more in Ch9)
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What Are the Mechanisms of
DNA Replication?
• Details of DNA replication (p. 119)
• The DNA helicase (an enzyme (a protein that acts as a
catalyst in a chemical reaction) that breaks apart the double
helix) separates and unwinds the DNA double helix.
• This forms a ‘bubble’ where nucleotide bases of the
parent strand are not longer paired.
• New base pairs form and knit a new double helix
down both sides due to a polymerase (an enzyme that
makes a DNA polymer)
• Then DNA Ligase (an enzyme that ties DNA together)
making one long complete DNA for both original strands
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replication forks
DNA helicase
DNA helicase
replication bubble
DNA polymerase #1
DNA
polymerase #2
DNA polymerase #1
continues along parental
DNA strand
continuous synthesis
DNA polymerase #2
leaves
DNA
polymerase #3
DNA polymerase #3
leaves
DNA
polymerase #4
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DNA ligase joins
daughter DNA strands
together
replication forks
DNA helicase
DNA helicase
replication bubble
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DNA polymerase #1
DNA
polymerase #2
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DNA polymerase #1
continues along parental
DNA strand
continuous synthesis
DNA polymerase #2
leaves
DNA
polymerase #3
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DNA polymerase #3
leaves
DNA
polymerase #4
DNA ligase joins
daughter DNA strands
together
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What Are the Mechanisms of
DNA Replication?
• Recap:
• DNA Helicase Separates the Parental
DNA Strands
• DNA Polymerase Synthesizes New
DNA Strands
• DNA Ligase Joins Together Segments
of DNA
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Chapter 9
• Gene Expression and Regulation
Minding your X and Y’s
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How Is the Information in
DNA Used in a Cell?
• Most Genes Contain Information for the
Synthesis of a Single Protein
– A gene is a stretch of DNA encoding the
instructions for the manufacture of one
protein.
– Proteins make the structures of the cell.
– One gene = one polypeptide (chain of
amino acids) (can call it a protein)
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RNA
• DNA ‘communicates’ with the
cytoplasm (cell guts) via RNA
• RNA Intermediaries Carry the Genetic
Information for Protein Synthesis
– A Comparison of DNA and RNA (p. 126)
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How Is the Information in DNA
Used in a Cell?
• Overview: Genetic Information Is
Transcribed into RNA, Then Translated
into Protein
– Genetic information flows from DNA to RNA
to protein (p. 126)
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gene
DNA
(nucleus)
(cytoplasm)
(a) Transcription
messenger RNA
(b) Translation
ribosome
protein
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What Is the Genetic Code?
•
•
•
•
•
A protein contains 20 amino acids
1 gene = 4 amino acid combinations
2 genes = 16 possible combinations
3 genes = 64 combinations – This works!
A Sequence of Three Bases Codes for an
Amino Acid
– The Genetic Code (Codons of mRNA) (p. 127)
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How Is the Information in a
Gene Transcribed into RNA?
• We now have the communication from DNA
to RNA to protein…. let’s look closer…
• Transcription Begins When RNA
Polymerase Binds to the Promoter of a
Gene
– Figure 9.2 Transcription is the synthesis of RNA
from instructions in DNA (p. 128)
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The steps…
1. initiation
- involves a promoter region at the beginning of the
gene, transcription is started
2. elongation
- involves the ‘body’ of the gene, the RNA strand is
elongated … Elongation Generates a Growing
Strand of RNA
3. termination
- involves the termination signal at the end of the
gene, RNA synthesis stops
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DNA
gene 1
gene 2
gene 3
Initiation
DNA
RNA
polymerase
promoter
RNA polymerase binds to the promoter region of DNA near the beginning of a gene, separating the double helix near
the promoter.
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Elongation
RNA
DNA template strand
RNA polymerase travels along the DNA template strand, catalyzing the addition of ribose nucleotides into an RNA
molecule. The nucleotides in the RNA are complementary to the template strand of the DNA.
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Termination
termination signal
At the end of a gene, RNA polymerase encounters a sequence of DNA called a termination signal. RNA polymerase
detaches from the DNA and releases the RNA molecule.
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Conclusion of transcription
RNA
After termination, the DNA completely rewinds into a double helix. The RNA molecule is free to move from the
nucleus to the cytoplasm for translation, and RNA polymerase may move to another gene and begin transcription
once again.
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gene
RNA
molecules
DNA
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How Is the Information in a
Gene Transcribed into RNA?
• Transcription Is Selective
– e.g. All DNA contains the information on
how to make insulin, but only pancreas
cells do it
– Proteins that bind to ‘control regions’ of the
DNA regulate what can and cannot be
copied by RNA – this defines cell function
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What Are the Functions of RNA?
• Cells synthesize three major types of RNA (p.
130) (in eukaryotic cells)
• All produced by transcription at the DNA
– messenger RNA (mRNA)
• Travel from DNA through pores in nuclear membrane into
the cytoplasm, binds to ribosomes, synthesizes proteins
– ribosomal RNA (rRNA)
• carry out translation making mRNA and make ribosomes
– transfer RNA (tRNA)
• carry/deliver amino acids to the ribosomes where they are
incorporated into protein making
• their ‘ends’ determine which amino acid they carry
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Messenger RNA (mRNA)
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Ribosome: contains
ribosomal RNA
(rRNA)
large
subunit
small
subunit
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catalytic site
tRNA/amino acid
binding sites
Transfer RNA (tRNA)
tyr
attached
amino acid
anticodon
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How Is the Information in
Messenger RNA Translated
into Protein?
• Translation Begins When tRNA
(transfer RNA) and mRNA (messenger
RNA) Bind to a Ribosome (protein
factory)
– Translation is the process of protein
synthesis (p. 132)
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Initiation:
amino acid
met
met
catalytic site
second tRNA
binding site
tRNA
initiation
complex
methionine
tRNA
mRNA
first tRNA
binding
site
large
ribosomal
subunit
small
ribosomal
subunit
A tRNA with an attached methionine
amino acid binds to a small
ribosomal subunit, forming
an initiation complex.
The initiation complex binds to an
mRNA molecule. The methionine
(met) tRNA anticodon (UAC) basepairs with the start codon (AUG) of
the mRNA.
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The large ribosomal subunit binds
to the small subunit. The methionine
tRNA binds to the first tRNA site on
the large subunit.
amino acid
met
methionine
tRNA
initiation
complex
small
ribosomal
subunit
A tRNA with an attached methionine
amino acid binds to a small
ribosomal subunit, forming
an initiation complex.
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met
tRNA
mRNA
The initiation complex binds to an
mRNA molecule. The methionine
(met) tRNA anticodon (UAC) basepairs with the start codon (AUG) of
the mRNA.
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catalytic site
first tRNA
binding
site
second tRNA binding site
large
ribosomal
subunit
The large ribosomal subunit binds
to the small subunit. The methionine
tRNA binds to the first tRNA site on
the large subunit.
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Elongation:
catalytic site
catalytic site
peptide
bond
initiator
tRNA detaches
ribosome moves one codon to right
The second codon of mRNA
(GUU) base-pairs with the
anticodon (CAA) of a second
tRNA carrying the amino acid
valine (val). This tRNA binds to
the second tRNA site on the
large subunit.
The catalytic site on the large subunit
catalyzes the formation of a peptide
bond linking the amino acids methionine
and valine. The two amino acids are now
attached to the tRNA in the second
binding position.
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The "empty" tRNA is released and
the ribosome moves down the mRNA,
one codon to the right. The tRNA that
is attached to the two amino acids is
now in the first tRNA binding site and
the second tRNA binding site is empty.
catalytic site
The second codon of mRNA
(GUU) base-pairs with the
anticodon (CAA) of a second
tRNA carrying the amino acid
valine (val). This tRNA binds to
the second tRNA site on the
large subunit.
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peptide
bond
The catalytic site on the large subunit
catalyzes the formation of a peptide
bond linking the amino acids methionine
and valine. The two amino acids are now
attached to the tRNA in the second
binding position.
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catalytic site
initiator
tRNA detaches
ribosome moves one codon to right
The "empty" tRNA is released and
the ribosome moves down the mRNA,
one codon to the right. The tRNA that
is attached to the two amino acids is
now in the first tRNA binding site and
the second tRNA binding site is empty.
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Termination:
catalytic site
completed
peptide
stop codon
The third codon of mRNA (CAU)
base-pairs with the anticodon
(GUA) of a tRNA carrying the
amino acid histidine (his). This
tRNA enters the second tRNA
binding site on the large subunit.
The catalytic site forms a new
peptide bond between valine
and histidine. A three-aminoacid chain is now attached to
the tRNA in the second binding
site. The tRNA in the first site
leaves, and the ribosome moves
one codon over on the mRNA.
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This process repeats until a
stop codon is reached; the
mRNA and the completed
peptide are released from the
ribosome, and the subunits
separate.
catalytic site
The third codon of mRNA (CAU)
base-pairs with the anticodon
(GUA) of a tRNA carrying the
amino acid histidine (his). This
tRNA enters the second tRNA
binding site on the large subunit.
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The catalytic site forms a new
peptide bond between valine
and histidine. A three-aminoacid chain is now attached to
the tRNA in the second binding
site. The tRNA in the first site
leaves, and the ribosome moves
one codon over on the mRNA.
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completed
peptide
stop codon
This process repeats until a
stop codon is reached; the
mRNA and the completed
peptide are released from the
ribosome, and the subunits
separate.
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How Is the Information in
Messenger RNA Translated
into Protein?
• Elongation Generates a Growing Chain
of Amino Acids
• A Stop Codon Signals Termination
– Complementary base pairing is critical to
decoding genetic information (p. 133)
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gene
DNA
etc.
complementary
DNA strand
template DNA
strand
etc.
codons
mRNA
etc.
anticodons
tRNA
etc.
amino acids
protein
methionine
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glycine
valine
etc.
gene
DNA
complementary
DNA strand
template DNA
strand
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etc.
etc.
codons
mRNA
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etc.
tRNA
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etc.
amino acids
protein
methionine
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glycine
valine
etc.
How Do Mutations Affect
Gene Function?
•
•
•
•
Base paring may be in error.
Proofreading enzymes sometimes miss something.
Atoms may move randomly and miss a connection
Mutations May Be
– Nucleotide Substitutions (point mutations)
• Individual nucleotides in DNA changed
– Insertions
• One or more nucleotides are added to the sequence
– Deletions
• One or more nucleotides are deleted from the sequence
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Attack of the mutant genes
• Mutations Affect Proteins in Different
Ways
– In most cases = harmful
– Deletions and insertions usually disastrous
– Often non-functional - the cell dies
– Effects of Mutations in the Hemoglobin
Gene (p. 135)
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How Do Mutations Affect
Gene Function?
• Mutations Are the Raw Material for Evolution
– They are the ultimate source of all differences
between people (and all living things)
– Rare change can be beneficial and help an
organism survive and reproduce when others of
it’s type die off.
– Extreme depths of time needed, many offspring
needed, mutation rate needs to be low
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Are All Genes Expressed?
• Gene Expression Differs from Cell to Cell
and over Time
– Only a small fraction of the 25,000 to 30,000
genes in each cell is being expressed at any
moment
• e.g. hair follicle cells vs. muscle vs. nerve cells
• pregnancy changes many functions of the female body
• Environmental Cues Influence Gene
Expression
– Seasonal changes/temperature/length of day etc.
trigger reproduction, hibernation, hair growth
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How Is Gene Expression Regulated?
• Regulatory Proteins That Bind to Promoters Alter the
Transcription of Genes
– Estrogen changes (season, attitude, etc.) regulates the expression
of the gene for albumin (protein in egg whites)
• Some Regions of Chromosomes Are Condensed and Not
Normally Transcribed
– RNA can’t access the tight coiling of that section of the DNA
molecule
• Entire Chromosomes May Be Inactivated and Not
Transcribed
– Male and females: Males have XY and females have XX
chromosomes. Females can produce twice as much protein as
males can, but this would be harmful, so one ‘X’ stays tightly coiled
up and inactive.
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Chapter 10
• The Continuity of Life: How Cells
Reproduce
To clone or not to clone… or
Send in the Clones
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Why Do Cells Divide?
• Cell Division Is Required for Growth and
Development
– Daughter cells are genetic copies of parent cells
(unless mutation occurs)
– Cells then differentiate based on function –
different genes are ‘turned on’ and ‘turned off’
• Cell Division Is Required for Asexual
Reproduction
– Figure 10.1 Asexual reproduction by mitotic cell
division (p. 145) a) Paramecium, b) yeast, c)
hydra budding, d) aspen trees
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Why Do Cells Divide?
• Meiotic Cell Division Is Required for
Sexual Reproduction
– Eukaryotic organisms (you)
– Fusion of gametes (sperm and egg)
• each has ½ the genetic code of parent
• humans = single cells
• plants = sometimes more complex organisms
first (see chapt 18)
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What Occurs During the
Prokaryotic Cell Cycle?
• (Bacteria and related stuff)
• Long growth period where DNA is
replicated inside. Plasma membrane
grows inward to between the two DNA.
• Rapid cell division – “Binary Fission”
• Cell grows – new cell membrane is built
• The prokaryotic cell cycle (p. 146)
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cell
division
cell growth and
DNA replication
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1
attachment
site
cell
wall
plasma
membrane
circular
DNA
The circular DNA double helix is attached
to the plasma membrane at one point.
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2
The DNA replicates and the two
DNA double helices attach to the
plasma membrane at nearby points.
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3
New plasma membrane is added
between the attachment points,
pushing them further apart.
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4
The plasma membrane grows inward
at the middle of the cell.
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5
The parent cell divides into two
daughter cells.
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What Occurs During the
Eukaryotic Cell Cycle?
• Two phases: interphase and cell division
• Interphase
– One copy of each chromosome, ½ of the
cytoplasm (including mitochondria, ribosomes,
and other organelles) are parceled out
– Most of the time spent here
– External signal needed to continue division, to
become a new cell type (differentiate) or die
– If signal is ‘go’ it replicates the DNA
– Cell can grow more after DNA replication
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Why did the cell divide across
the road?
• Two kinds of eukaryotic cell division:
– Mitotic cell division
•
•
•
•
•
Nuclear division first (mitosis)
Cytoplasmic division second (cytokinesis)
Important in asexual reproduction
Makes more cells in growing/repairing bodies
Identical copies of DNA in both cells
– Meiotic cell division
• Needed in animal sexual reproduction
• Special nuclear division called meiosis and two rounds
of cytokinesis to produce 4 daugher cells that become
gametes (egg or sperm)
• Each has ½ the genetic material/strands of the parent
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cell growth and
differentiation
cell
growth
interphase
synthesis
of DNA;
chromosomes
are duplicated
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What Occurs During the
Eukaryotic Cell Cycle?
• The Life Cycles of Eukaryotic Organisms
Include Both Mitotic and Meiotic Cell
Division
– Mitotic and meiotic cell division in the human life
cycle (p. 148)
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mitotic cell division,
differentiation, and growth
adults
baby
mitotic cell division,
differentiation,
and growth
meiotic cell
division in
ovaries
embryo
meiotic cell
division in
testes
egg
mitotic
cell division,
differentiation,
and growth
fertilized
egg
sperm
fertilization
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How Is DNA in Eukaryotic
Cells Organized into
Chromosomes?
• Eukaryotic Chromosomes Consist of
DNA Bound to Proteins
– DNA stretched out would be 6 feet long!
– DNA is usually extended so RNA can get to
it
– Chromosomes (DNA + organization
proteins) Condense During Cell Division
due to the action of these proteins
• A Chromosome Contains Many Genes
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Chromosomes to Genes
• Sequences of base sequences
(nucleotides) are called Genes.
• DNA is made up of sequences of Genes.
• A single DNA double helix may contain
hundreds or thousands of genes, each
occupying a specific place on a
chromosome.
• Chromosomes = the DNA double helix
with it’s organization proteins
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A couple more definitions
• Centromere = link point of duplicated
chromosome before division takes
place
• Sister chromatid = the copy before
division takes place
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genes
centromere
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How Is DNA in Eukaryotic Cells
Organized into Chromosomes?
• Duplicated Chromosomes Separate
During Cell Division (following pictures)
– Figure 10.5 Human chromosomes during
mitosis (p. 149)
– Sister chromatids and duplicated
chromosomes (p. 149)
– Independent daughter chromosomes
(p. 149)
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sister chromatids
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centromere
sister
chromatids
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duplicated
chromosome
independent
daughter
chromosomes
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How Is DNA in Eukaryotic
Cells Organized into
Chromosomes?
• Eukaryotic Chromosomes Usually Occur in Pairs
– As seen in the karyotype (photographic method
showing chromosomes) of a human male (p. 149) in
the next frame…
– Genes are stained different colors…
– In the human body each cell has 2 sets of 23 pairs OR
46 chromosomes
– 1-22 are copies (autosomes)
– 23 = the sex chromosomes XX = female XY=male
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How Is DNA in Eukaryotic
Cells Organized into
Chromosomes?
– Not All Cells Have Paired Chromosomes
– Reproductive cells= sperm and egg
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Plant Cell divison
• The cell cycle in a plant cell (p. 151)
– 1st step (review) nuclear division
– 2nd step (review) cytoplasmic division
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Interphase in a seed cell: The
chromosomes (blue) are in the thin,
extended state and appear as a mass in
the center of the cell. The spindle
microtubules (red) extend outward from
the nucleus to all parts of the cell.
Anaphase: Sister chromatids have
separated, and one set has moved toward
each pole.
Late prophase: The chromosomes
(blue) have condensed and attached to
the spindle microtubules (red).
Telophase: The chromosomes have
gathered into two clusters, one at
the site of each future nucleus.
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Metaphase: The chromosomes have
moved to the equator of the cell.
Resumption of interphase: The
chromosomes are relaxing again into their
extended state. The spindle microtubules
are disappearing, and the microtubules of
the two daughter cells are rearranging into
the interphase pattern.
Interphase in a seed cell: The
chromosomes (blue) are in the thin,
extended state and appear as a mass in
the center of the cell. The spindle
microtubules (red) extend outward from
the nucleus to all parts of the cell.
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Late prophase: The chromosomes
(blue) have condensed and attached to
the
spindle
microtubules
(red).
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Metaphase: The chromosomes have
moved to the equator of the cell.
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Anaphase: Sister chromatids have
separated, and one set has moved toward
each pole.
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Telophase: The chromosomes have
gathered into two clusters, one at
the site of each future nucleus.
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Resumption of interphase: The
chromosomes are relaxing again into their
extended state. The spindle microtubules
are disappearing, and the microtubules of
the two daughter cells are rearranging into
the interphase pattern.
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Animal Cell division
• Mitotic cell division in an animal cell (p.
152 and 153)
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INTERPHASE
nuclear
envelope
MITOSIS
chromatin
nucleolus
pole
condensing
chromosomes
spindle
microtubules
centromere
centriole
pairs
LATE INTERPHASE
Duplicated chromosomes in
relaxed state; duplicated
centrioles remain clustered.
beginning of
spindle formation
EARLY PROPHASE
Chromosomes condense
and shorten; spindle
microtubules begin to form
between separating
centriole pairs.
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pole
LATE PROPHASE
Nucleolus disappears;
nuclear envelope breaks
down; spindle microtubules
attach to each sister
chromatid.
METAPHASE
Spindle microtubules line
up chromosomes at cell's
equator.
INTERPHASE
"free" spindle
fibers
chromosomes
extending
ANAPHASE
Sister chromatids separate
and move to opposite poles
of the cell; spindle
microtubules push poles
apart.
nuclear envelope
re-forming
TELOPHASE
One set of chromosomes
reaches each pole and
relaxes into extended state;
nuclear envelopes start to
form around each set;
spindle microtubules begin
to disappear.
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CYTOKINESIS
Cell divides in two; each
daughter cell receives one
nucleus and about half of
the cytoplasm.
INTERPHASE OF
DAUGHTER CELLS
Spindles disappear, intact
nuclear envelopes form,
chromosomes extend
completely, and the
nucleolus reappears.
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INTERPHASE
nuclear
envelope
chromatin
nucleolus
centriole
pairs
LATE INTERPHASE
Duplicated chromosomes in
relaxed state; duplicated
centrioles remain clustered.
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MITOSIS
condensing
chromosomes
beginning of
spindle formation
EARLY PROPHASE
Chromosomes condense
and shorten; spindle
microtubules begin to form
between separating
centriole pairs.
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pole
centromere
pole
LATE PROPHASE
Nucleolus disappears;
nuclear envelope breaks
down; spindle microtubules
attach to each sister
chromatid.
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spindle
microtubules
METAPHASE
Spindle microtubules line
up chromosomes at cell's
equator.
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"free" spindle
fibers
ANAPHASE
Sister chromatids separate
and move to opposite poles
of the cell; spindle
microtubules push poles
apart.
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chromosomes
extending
nuclear envelope
re-forming
TELOPHASE
One set of chromosomes
reaches each pole and
relaxes into extended state;
nuclear envelopes start to
form around each set;
spindle microtubules begin
to disappear.
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CYTOKINESIS
Cell divides in two; each
daughter cell receives one
nucleus and about half of
the cytoplasm.
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INTERPHASE
INTERPHASE OF
DAUGHTER CELLS
Spindles disappear, intact
nuclear envelopes form,
chromosomes extend
completely, and the
nucleolus reappears.
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Close-up on the last step cytokinesis
• During Cytokinesis, the Cytoplasm Is Divided
between Two Daughter Cells
– Cytokinesis in an animal cell (p. 156)
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1 Microfilaments form
a ring around the cell's
equator.
2 The microfilament ring
contracts, pinching
in the cell's “waist.”
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3 The waist completely
pinches off, forming
two daughter cells.
Plant Cytokinesis
• It’s the same for plants…
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Golgi complex
cell wall
plasma membrane
carbohydratefilled vesicles
1 Carbohydrate-filled vesicles
bud off the Golgi complex and
move to the equator of the cell.
2 Vesicles fuse to form a new
cell wall (red) and plasma
membrane (yellow) between
daughter cells.
Copyright © 2005 Pearson Prentice Hall, Inc.
3 Complete separation of
daughter cells.
Hello Dolly
• Review- two types of cell division: mitotic
(two identical cells, double helix) and
meiotic (four cells, single strand of DNA
ready for other sex’s contribution)
• Cloning common, i.e. naval oranges,
seedless grapes etc. (no seeds- we clone)
• Very disastrous to most genetic material
using present day technology
Copyright © 2005 Pearson Prentice Hall, Inc.
Making Dolly
• Hit-or-miss.
• Adult cloning the goal – known traits
• 277 tries to make Dolly, and 87 to make
CC the first cloned cat.
• Nucleotides sequences at the end of
chromosomes shorten each time a cell
divides. Dolly’s nucleotide sequences
were already middle-aged.
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Finn Dorset ewe
donor cell
from udder
electric pulse
fused cells
1 Cells from the udder of a Finn Dorset ewe
are grown in culture with low nutrient levels.
The starved cells stop dividing and enter the
non-dividing G0 phase of the cell cycle. The
starved cells stop dividing.
Blackface ewe
egg
cell
2 Meanwhile, the nucleus is sucked out of an
unfertilized egg cell taken from a Scottish
Blackface ewe. This egg will provide cytoplasm
and organelles but no chromosomes.
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nucleus is
removed
DNA
3 The egg cell without a nucleus and the
quiescent udder cell are placed side by
side in a culture dish. An electric pulse
stimulates the cells to fuse and initiates
mitotic cell division.
4 The cell divides, forming an embryo
that consists of a hollow ball of cells.
5 The ball of cells is implanted into
the uterus of another Blackface ewe.
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6 The Blackface ewe gives birth to
Dolly, a female Finn Dorset lamb, a
genetic twin of the Finn Dorset ewe.
How Does Meiotic Cell Division
Produce Haploid Cells?
• Meiosis Produces Four Haploid Daughter
Nuclei (this is to produce reproduction cells
--- sperm and eggs)
• Meiosis I Separates Homologous
Chromosomes into Two Haploid Daughter
Nuclei
– During Prophase I, Homologues Pair Up
• Meiotic cell division in an animal cell (p. 158 and 159)
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MEIOSIS I
paired homologous
chromosomes
chiasma
recombined
chromosomes
spindle
microtubule
Prophase I. Duplicated
chromosomes condense.
Homologous chromosomes
pair up and chiasmata occur
as chromatids of homologues
exchange parts. The nuclear
envelope disintegrates, and
spindle microtubules form.
Late in prophase,
microtubules attach to
chromosomes.
Metaphase I. Paired
homologous chromosomes
line up along the equator of
the cell. One homologue of
each pair faces each pole
of the cell.
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Anaphase I. Homologues
separate, one member of
each pair going to each pole
of the cell. Sister chromatids
do not separate.
Telophase I. Spindle
microtubules disappear. Two
clusters of chromosomes have
formed, each containing one
member of each pair of
homologues. The daughter nuclei
are therefore haploid. Cytokinesis
commonly occurs at this stage.
There is little or no interphase
between meiosis I and meiosis II.
10.6 How Does Meiotic Cell
Division Produce Haploid Cells?
• Meiosis II Separates Sister Chromatids into Four
Haploid Daughter Cells
• (Next frame)
• Then…A Comparison of Mitotic and Meiotic Cell
Divisions in Animal Cells (p. 161)
• (Following Frame)
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MEIOSIS II
Prophase II.
Spindle microtubules
re-form and attach to
the sister chromatids.
Metaphase II.
Chromosomes line
up along the equator,
with sister chromatids
of each chromosome
attached to spindle
microtubules that lead
to opposite poles.
Anaphase II.
Chromatids separate
into independent
daughter chromosomes,
one former chromatid
moving toward each
pole.
Copyright © 2005 Pearson Prentice Hall, Inc.
Telophase II.
Chromosomes finish
moving to opposite
poles. Nuclear
envelopes re-form,
and the chromosomes
become extended
again (not shown here).
Four haploid cells.
Cytokinesis results in
four haploid cells, each
containing one member
of each pair of
homologous
chromosomes (shown
here in condensed state).
Copyright © 2005 Pearson Prentice Hall, Inc.
How Do Meiotic Cell Division
and Sexual Reproduction
Produce Genetic Variability?
• Shuffling of Homologues Creates Novel
Combinations of Chromosomes
– Random assortment of homologues (pairs of
similar chromosomes that match during meiosis)
– Chromosomes align (p. 161) in different
combinations during metaphase 1 – example next
slide: 4 sets of 3 can create 8 combinations
during anaphase I (p. 161)
– Random-ness!
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Copyright © 2005 Pearson Prentice Hall, Inc.
Copyright © 2005 Pearson Prentice Hall, Inc.
How Do Meiotic Cell Division
and Sexual Reproduction
Produce Genetic Variability?
• Crossing Over Creates Chromosomes with
Novel Combinations of Genetic Material
– Each man may product 100 million sperm a day,
but no two may ever be the same!
• Fusion of Gametes Creates Genetically
Variable Offspring
– Mix this with the same variations in the woman’s
egg, and you have genetic variations!!
Copyright © 2005 Pearson Prentice Hall, Inc.
Chapter 11
• Patterns of Inheritance
• It’s all in the genes…
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What Is the Physical Basis of
Inheritance?
• (review) Genes Are Sequences of Nucleotides at
Specific Locations on Chromosomes
• Inheritance is the process where genes are passed
on to offspring.
• The home of a gene on a chromosome is called it’s
locus (plural loci)
• Different nucleotide sequences in the same locus on
two homologous chromosomes are called alleles.
(pronounced a-leels)
• Different alleles may produce different characteristics
such
as
brown
vs. blue
Copyright
© 2005
Pearson Prentice
Hall, Inc.eyes.
Alleles
• An Organism’s Two Alleles May Be the
Same or Different
– The relationships among genes, alleles,
and chromosomes (p. 168)
– Same genes on pairs of chromosomes =
alleles are homozygous
– Different genes on pairs of chromosomes=
alleles are heterozygous (also called a
hybrid)
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chromosome 1
from tomato
pair of
homologous
chromosomes
homozygous
allele of the
genes here
heterozygous
allele of the
genes here
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How Were the Principles of
Inheritance Discovered?
• Gregor Mendel (p. 168) mid-1800’s
• Austrian monk
• (The dude…)
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Copyright © 2005 Pearson Prentice Hall, Inc.
How Were the Principles of
Inheritance Discovered?
• Doing It Right: The Secrets of Mendel’s
Success
– Flowers of the edible pea (p. 169)
– 1) choose the right organism to study
– 2) designed his experiments carefully
– 3) analyzed his data properly
– The plant is self fertilizing – no mixing with
other plant DNA
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intact pea flower
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flower dissected to show
reproductive structures
How Are Single Traits
Inherited?
• He forced cross fertilization
• Found true breeding purple and white
flowers (true breeding= all offspring
always have this trait)
• Mendel's Peas: F1 Generation (p. 169)
• Mendel's Peas: F2 Generation (p. 170)
Copyright © 2005 Pearson Prentice Hall, Inc.
pollen
Parental
generation (P)
pollen
cross-fertilize
true-breeding,
purple-flowered
plant
true-breeding,
white-flowered
plant
First-generation
offspring (F1)
all purple-flowered
plants
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First
generation
offspring (F1)
self-fertilize
Second
generation
offspring (F2)
3/4 purple
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1/4 white
How Are Single Traits
Inherited?
• 11.3.1 The Pattern of Inheritance of Single Traits
Can Be Explained by the Inheritance of Alleles of a
Single Gene
• See following sequence of slides:
– Mendel's Peas: Gametes from a homozygous parent (p. 170)
– Mendel's Peas: Gametes from a heterozygous parent (p.
171)
– Mendel's Peas: Allele production (p. 171)
– Mendel's Peas: Heterozygote offspring from dominant and
recessive parents (p. 171)
– Mendel's Peas: F1 alleles to F2 generation (p. 171)
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homozygous parent
A
A
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gametes
A
A
heterozygous parent
A
a
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gametes
A
a
purple parent
P
PP
P
all P sperm and eggs
white parent
pp
p
p
all p sperm and eggs
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F1
offspring
sperm
eggs
P
p
Pp
P
Pp
or
p
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gametes from
F1 plants
F2
offspring
sperm
eggs
P
P
PP
P
p
Pp
p
P
Pp
p
p
pp
Copyright © 2005 Pearson Prentice Hall, Inc.
How Are Single Traits
Inherited?
• Simple “Genetic Bookkeeping” Can
Predict Genotypes and Phenotypes of
Offspring
– The Punnett square method (p. 172)
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Pp
self-fertilize
p
1
—
2
1
—
eggs
1
—
p
2
P
2
1
—
PP
4
1
—
1
—
Pp
4
p
2
1
—
4
pP
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1
—
4
pp
How Are Single Traits
Inherited?
• Mendel’s Hypothesis Can Predict the
Outcome of New Types of Single-Trait
Crosses
– The combinations yield probabilities that
are observable when you grow many
offspring
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How Are Multiple Traits Inherited?
(Making it more complex—of course)
• E.G. Seeds can be colored (yellow or
green) and smooth or wrinkled.
• He concluded that multiple traits are
inherited independently!
• Dominate traits always win
• Recessive traits always loose (unless they
are all that is there)
• (Genes, but he didn’t know it)
• Traits of pea plants that Mendel studied (p.
173)
Copyright © 2005 Pearson Prentice Hall, Inc.
Seed
shape
Seed
color
smooth
wrinkled
yellow
green
inflated
constricted
green
yellow
purple
white
at leaf
junctions
at tips of
branches
tall
(1.8 to
2 meters)
dwarf
(0.2 to 0.4
meters)
Pod
shape
Pod
color
Flower
color
Flower
location
Plant
size
Copyright © 2005 Pearson Prentice Hall, Inc.
How Are Multiple Traits
Inherited?
• Mendel Concluded That Multiple Traits Are
Inherited Independently
– Predicting genotypes and phenotypes for a cross
between parents that are heterozygous for two
traits (p. 173)
– Independent assortment of alleles (p. 174)
–
–
–
–
S = dominant gene for smooth seed shape
s = recessive gene for wrinkled seed shape
Y = dominate gene for yellow seed
y = recessive gene for green seed
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SsYy
self-fertilize
eggs
1
—
4
1
—
4
SY
1
—
4
Sy
1
—
4
sY
1
—
4
sy
Copyright © 2005
SY
1
—
4
Sy
1
—
4
sY
1
—
4
sy
1
—
16
SSYY
1
—
16
SSYy
1
—
16
SsYY
1
—
16
SsYy
1
—
16
SSyY
1
—
16
SSyy
1
—
16
SsyY
1
—
16
Ssyy
1
—
16
sSYY
1
—
16
sSYy
1
—
16
ssYY
1
—
16
ssYy
1
— sSyy
Hall,16
Inc.
1
—
16
ssyY
1
—
16
ssyy
1
— sSyY
16 Prentice
Pearson
pairs of alleles on homologous
chromosomes in diploid cells
chromosomes replicate
replicate homologous
pair during metaphase
of meiosis I,
orienting like this
or like this
meiosis I
meiosis II
SY
sy
Sy
independent assortment produces four equally
likely allele combinations during meiosis
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sY
How Are Multiple Traits
Inherited?
• In an Unprepared World, Genius May
Go Unrecognized
– Presented his theories in 1865 and 1866
– No impression made on the world during
his life (he died in 1884)
– 1900 – three biologists rediscovered his
principles independently
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flower color gene
pollen shape gene
purple
allele, P
long
allele, L
red
allele, p
round
allele, I
Copyright © 2005 Pearson Prentice Hall, Inc.
How Are Genes Located on
the Same Chromosome
Inherited?
• Chromosomes NOT individual genes are
separated during meiosis
• Genes on the same chromosomes tend to
be inherited together! Called Genetic
Linkage
• Crossing Over (review – in prophase I of
meiosis) Can Create New Combinations of
Linked Alleles
Copyright © 2005 Pearson Prentice Hall, Inc.
How Is Sex Determined?
• Special chromosome for sex
• X and Y
• XX = female XY = male
Can’t have YY
• Photomicrograph of human sex
chromosomes (p. 175) [next slide]
• Sex determination in mammals (p. 176)
[following slide]
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Y chromosome
X chromosome
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female parent
eggs
male parent
female offspring
male offspring
Copyright © 2005 Pearson Prentice Hall, Inc.
How Are Sex-Linked Genes
Inherited?
Simple… the genes found on the X or Y chromosomes are those
related to sexual differences.
• In many animals, the Y chromosome contains only a few genes
• Human Y = 78 genes found, most matter to human reproduction
(all are expressed since they don’t match to the X)
– Also color vision, blood clotting, and certain structural proteins in muscles
• Human X = > 1000 genes, few of which matter to human
reproduction (dominate and recessive rules apply since genes do
match)
Copyright © 2005 Pearson Prentice Hall, Inc.
Do the Mendelian Rules of
Inheritance Apply to All Traits?
• Incomplete Dominance Produces
Intermediate Phenotypes
– Figure 11.10 Incomplete dominance
(p. 177)
– Some of both trait CAN show up in mixes
– Snapdragons for example
Copyright © 2005 Pearson Prentice Hall, Inc.
P:
RR
R´R´
RR´
RR´
F1:
F2:
1
—
R
2
1
—
2
1
R´
2
RR
4
1
1
—
R
—
—
eggs
1
—
RR´
4
R´
2
1
—
4
RR´
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1
—
4
R´R´
Do the Mendelian Rules of
Inheritance Apply to All Traits?
• A Single Gene May Have Multiple Alleles
– e.g. Over all humans, many eye colors, hair
colors etc.
– Table 11.1 Human Blood Group Characteristics
(p. 178)
•
•
•
•
A, B, AB, and O result from 3 alleles
A and B make different ‘glycoproteins’
O is non-functional and doesn’t make the glycoproteins
A & B are dominant over O
Copyright © 2005 Pearson Prentice Hall, Inc.
Copyright © 2005 Pearson Prentice Hall, Inc.
Do the Mendelian Rules of
Inheritance Apply to All Traits?
• A Single Trait May Be Influenced by Several
Genes = polygenic inheritance
• A Single Gene May Have Multiple Effects on
Phenotype = pleiotropy
• The Environment Influences the Expression of
Genes
– Environmental influence on phenotype (p. 178)
– Himalayan rabbit has the genotype for black fur pigment,
but is inactive above 93F (34C).
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How Are Human Genetic
Disorders Investigated?
• Family records over many generations
(medical problems) can predict the
likelihood of diseases…
• Family pedigrees (p. 180)
Copyright © 2005 Pearson Prentice Hall, Inc.
A pedigree for a dominant trait



A pedigree for a recessive trait


?
?
?
?

V
?
?
?
How to read pedigrees
, ,  = generations
= female
= male
= parents
= offspring
?
or
= shows trait
or
= does not show trait
or
= known carrier (heterozygote) for
or
recessive trait
?
= cannot determine genotype from pedigree
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A pedigree for a dominant trait



Copyright © 2005 Pearson Prentice Hall, Inc.
A pedigree for a recessive trait


?
?
?

V
?
?
Copyright © 2005 Pearson Prentice Hall, Inc.
?
?
How Are Single-Gene
Disorders Inherited?
• Some Human Genetic Disorders Are
Caused by Recessive Alleles
– Two recessive genes add and bring out hidden
diseases
– Everyone carries 5-15 harmful recessive genes
– If both parents have a recessive gene, the
children have a 50/50 chance of getting the
disease
Copyright © 2005 Pearson Prentice Hall, Inc.
Sickle-cell Anemia
– A Defective Allele for Hemoglobin
Synthesis Causes Sickle-Cell Anemia
• Sickle-cell anemia (p. 181)
• When O2 is low, hemoglobin molecules clump
deforming blood cells, can clog capillaries
• One recessive gene = half normal, half sickled
• 8% of African-Americans have the disease,
almost 0% whites have it
– Sickle cell blood cells are less susceptible to Malaria
– Natural Selection favored survival of sickle-cell
anemia
Copyright © 2005 Pearson Prentice Hall, Inc.
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How Are Single-Gene
Disorders Inherited?
• Some Human Genetic Disorders Are Caused
by Dominant Alleles
– Huntington disease, protein that wastes the brain
starting about age 30-50
• Some Human Genetic Disorders Are SexLinked
– Hemophilia – deficiency of one of the proteins
needed for blood clotting
– Color blindness, a sex-linked recessive trait
(p. 183)
Copyright © 2005 Pearson Prentice Hall, Inc.

maternal
grandfather

mother father
aunts

sister
G. Audesirk
T. Audesirk
V
daughter
=
colorblind
=
heterozygous carrier female,
normal color vision
normal color vision (not carrier)
or
or
=
Copyright © 2005 Pearson Prentice Hall, Inc.
Copyright © 2005 Pearson Prentice Hall, Inc.
How Do Errors in
Chromosome Number Affect
Humans?
• Abnormal Numbers of Sex Chromosomes
Cause Some Disorders
– Usually you get XX, or XY
– Nondisjunct sperm = XX, YY or XY
– Females can make= XX or O eggs (no sex
chromosomes)
– Children = XO, XXX, XXY, XYY
(must have X to live)
– Effects of Nondisjunction of the Sex
Chromosomes During Meiosis (p. 183)
Copyright © 2005 Pearson Prentice Hall, Inc.
Copyright © 2005 Pearson Prentice Hall, Inc.
How Do Errors in
Chromosome Number Affect
Humans?
– Turner Syndrome (XO) puberty (1 in 3000 females)  hormone
deficiencies, no menstruation, no enlarged breasts, nonfunctional ovaries, short stature, folds in skin around neck,
increased heart disease, kidney defects, hearing loss,
hemophilia, color blindness
– Trisomy X (XXX) (1 in 1000 females)  tend to be tall, can have
below normal intelligence, ARE fertile – usually have XX and XY
children (can’t be passed on- not understood)
– Klinefelter Syndrome (XXY) (1 in 1000 males)  most never
realize they have an extra X. At puberty can get partial breast
development, broadening of the hips, low sperm count. Usually
discovered when couples can’t have children.
– Jacob Syndrome (XYY) (1 in 1000 males)  High testosterone
levels, severe acne, are tall (1/3rd are > 6 feet tall), slightly lower
IQ than XY males.
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More on extra X’s and Y’s
• Abnormal Numbers of Autosomes Cause Some
Disorders
– Most with extra copies of other chromosomes abort
spontaneously
– Three copies of chromosome 13, 18, 21 can at least be born
– Trisomy 21 (Down Syndrome)
– An extra copy of the 21st chromosome
• Trisomy 21, or Down syndrome (p. 185)
• Down syndrome frequency increases with maternal age (p. 185)
• Weak muscle tone, small mouth held open by relatively large tongue,
distinctively shaped eyelids, low resistance to infections diseases,
heart malformations, varying degrees of mental retardation- often
severe.
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number per 10,000 births
Incidence of Down Syndrome
age of mother (years)
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Chapter 12
• Biotechnology
• If the glove don’t fit, you must acquit.
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What Is Biotechnology?
• Any use or alteration of organisms, cells, or
biological molecules to achieve practical goals.
• Yeast has been bred for 10,000 years to make
bread, beer, wine.
• Squash has been bred for about 10,000 years as
well.
• Putting in genes from other organisms =
recombinant DNA
• Organisms that express DNA form other species
are called transgenic or genetically modified
organisms (GMOs)
• Forensic uses are also included in biotechnology.
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How Does DNA Recombine in
Nature?
• DNA is NOT constant in nature.
• Sexual Reproduction Recombines DNA
• Transformation May Combine DNA
from Different Bacterial Species
– And from other species
– Recombination in bacteria (p. 195)
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Bacterium
bacterial
chromosome
plasmid
Transformation with DNA fragment
bacterial
chromosome
Transformation with plasmid
bacterial
chromosome
DNA
fragments
plasmid
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How Does DNA Recombine in
Nature?
• Viruses May Transfer DNA between Species
– Viruses may transfer genes between cells
(p. 196)
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virus
viral DNA
2 Virus enters host cell.
host cell
3 Virus releases its DNA into
host cell; some viral DNA (red)
may be incorporated into the
host cell’s DNA (blue).
host cell DNA
1 Virus attaches to
susceptible host cell.
viral DNA
“hybrid virus”
6 Host cell bursts, releasing
newly assembled viruses.
when “hybrid viruses” infect a
second cell, they may transfer
genes from the first cell to the
second cell.
viral proteins
4 Viral genes encode synthesis
Of viral proteins and viral gene
Replication. Some host cell DNA
May attach to replicated viral
DNA (red/blue).
5 New viruses assemble; host
cell DNA is carried by “hybrid
viruses.”
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virus
viral DNA
host cell
host cell DNA
1 Virus attaches to
susceptible host cell.
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2 Virus enters host cell.
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3 Virus releases its DNA into
host cell; some viral DNA (red)
may be incorporated into the
host cell’s DNA (blue).
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viral DNA
viral proteins
4 Viral genes encode synthesis
Of viral proteins and viral gene
Replication. Some host cell DNA
May attach to replicated viral
DNA (red/blue).
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“hybrid virus”
5 New viruses assemble; host
cell DNA is carried by “hybrid
viruses.”
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6 Host cell bursts, releasing
newly assembled viruses.
when “hybrid viruses” infect a
second cell, they may transfer
genes from the first cell to the
second cell.
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How Is Biotechnology Used
in Forensics?
• A single strand (or small samples) of DNA is not
enough to test… we need to make copies…
• The Polymerase Chain Reaction Amplifies DNA
– PCR copies a specific DNA sequence (p. 197)
– Thomas Brock surveys Mushroom Spring (p. 198)
• (hot water allows reproduction using Thermus aquaticus- lives in
these hot springs…allows this process)
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One PCR cycle
90 ºC
original
DNA
50 ºC
DNA
polymerase
primers
1 Heating
separates
DNA strands.
72 ºC
2 Cooling allows
primers and
DNA polymerase
to bind.
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new DNA
strands
3 New DNA
strands are
synthesized.
Each PCR cycle doubles the number of copies of the DNA
DNA
fragment
to be
amplified.
PCR
cycles
DNA
copies
1
1
2
3
4 etc.
2
4
8
16 etc.
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Copyright © 2005 Pearson Prentice Hall, Inc.
How Is Biotechnology Used in
Forensics?
• Differences in Short DNA Segments Can
Identify Individuals
– Don’t need the whole strand, short strands can do
a great job!
– Figure 12.4 Short tandem repeats (STR) (p. 198)
– 1999 British and American law enforcement
agencies use a standard set of 10-13 STR
– A perfect match means less than a 1 in a
1,000,000,000,000 chance of mistaken identity
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8 side-by-side (tandem) repeats
of the same 4-nucleotide sequence,
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How Is Biotechnology Used in
Forensics?
• Another technique…
• Gel Electrophoresis Separates DNA Segments
– Figure 12.5 Gel electrophoresis is used to separate and
identify segments of DNA (p. 199)
• DNA Probes Are Used to Label Specific
Nucleotide Sequences (colors what we want to
see)
• A DNA Fingerprint Is Unique to Each Person
– Figure 12.6 DNA fingerprinting (p. 200)
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power supply
pipetter
�
�
gel
wells
�
�
DNA samples are pipetted into wells
(shallow slots) in the gel. Electrical current
is sent through the gel (negative at end
with wells, positive at opposite end).
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�
�
DNA bands
(not yet visible)
�
Electrical current moves DNA
segments through the gel. Smaller
pieces of DNA move farther toward the
positive electrode.
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�
gel
�
�
�
Gel is placed on special nylon
paper. Electrical current drives
DNA out of gel onto nylon.
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�
nylon
paper
solution of DNA
�
� probes (red)
nylon paper
�
�
Nylon paper with DNA is bathed in a solution of labeled DNA probes (red) that
are complementary to specific DNA segments in the original DNA sample.
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�
�
�
�
Complementary DNA segments are labeled by probes
(red bands).
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Penta D
CSF
D16
D7
D13
D5
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Number of repeats
STR name
Number of repeats
D16: an STR on chromosome 16
DNA samples from
13 different people
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How Is Biotechnology Used in
Agriculture?
• Many Crops Are Genetically Modified
– 34% of the corn, 71% of the cotton, 75% of
soybeans
– Most are transgenic – have other plant
genes spliced in
– The Desired Gene Is Cloned
– Herbicides kill plants by inhibiting enzymes
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How to pull a gene…
– Restriction Enzymes Cut DNA at Specific
Nucleotide Sequences
• Restriction enzymes cut DNA at specific
nucleotide sequences (p. 201)
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How Is Biotechnology Used in
Agriculture?
– Cutting Two Pieces of DNA with the Same
Restriction Enzyme Allows the Pieces to Be
Joined Together
• Using plasmids to insert DNA into a plant cell (p. 201)
• Bt gene from anther plant repels insects
• Bt plants resist insect attack (p. 202)
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DNA including Bt gene (blue)
Ti Plasmid
Cut both with the same restriction enzyme.
Mix Bt gene and plasmid; add DNA ligase to seal DNA.
Transform bacterium with recombinant plasmid.
bacterium
bacterial
chromosome
plasmids
Infect plant cell with transgenic bacterium
Bt gene is inserted into plant chromosome.
Bt gene
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DNA including Bt gene (blue)
Ti Plasmid
Cut both with the same restriction enzyme.
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Mix Bt gene and plasmid; add DNA ligase to seal DNA.
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Transform bacterium with recombinant plasmid.
bacterium
bacterial
chromosome
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plasmids
Infect plant cell with transgenic bacterium
Bt gene is inserted into plant chromosome.
Bt gene
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NewLeaf®
beetle-resistant
transgenic potatoes
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non-resistant
potatoes
How Is Biotechnology Used in
Agriculture?
• Genetically Modified Animals May Be Useful
in Agriculture and Medicine
– Transgenic salmon (p. 202)
– What if the salmon gets into the wild?
– Researchers developing animals that produce
medicine as well.
• There are sheep whose milk contains a protein (alpha
1-antitrypsin) may prove valuable in treating cystic
fibrosis.
• Potatoes with flu vaccine, polio vaccine, etc.
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How Is Biotechnology Used to
Learn About the Human
Genome?
• Screening children at the embryo
phase?
• Screening prospective parents or even
couples for diseases that ‘might’
arise…
• Treating early life?
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How Is Biotechnology Used
for Medical Diagnosis and
Treatment?
• Prenatal cell sampling techniques (p. 206)
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amniocentesis
chorionic villi
placenta
amniotic
fluid
centrifuge
fetus
fluid: composition
analysis
cells: sex
determination,
biochemical and
enzymatic studies
cells culture: biochemical
studies, chromosomal
analysis, analysis using
recombinant DNA
methods
uterus
vagina
chorionic
villus sampling
(by suction)
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How Is Biotechnology Used
for Medical Diagnosis and
Treatment?
• DNA Technology Can Be Used to
Diagnose Inherited Disorders
– Restriction Enzymes Cut Different Alleles at
Different Locations
• Diagnosing sickle-cell anemia with restriction
enzymes (p. 204)
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Mst II cuts a normal globin allele in 2 places, but cuts the
sickle-cell allele in 1 place.
Mst II
Mst II
Mst II
normal
globin allele
DNA probe
Mst II
Mst II
sickle-cell
globin allele
DNA probe
Gel electrophoresis of globin alleles
AA
AS
SS
large
small
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AA = homozygous normal
AS = heterozygote
SS = homozygous sickle-cell
How Is Biotechnology Used
for Medical Diagnosis and
Treatment?
– Different Alleles Bind to Different DNA Probes
• Diagnosing cystic fibrosis with a DNA array (p. 204)
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complementary DNA
for normal allele
rows of complementary
DNA segments for
various mutant alleles
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How Is Biotechnology Used for
Medical Diagnosis and Treatment?
• DNA Technology Can Be Used to Treat
Disease
– Several medically important proteins are
now routinely made in bacteria.
– Insulin first and most prevalent
– Table 12.1 Examples of Products
Produced by Recombinant DNA Methods
(p. 205)
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How Is Biotechnology Used for
Medical Diagnosis and Treatment?
– Using Biotechnology to Treat Cystic
Fibrosis
• Devastating disease in the lungs where the
lack of chloride transport causes thin, watery
fluid lining in lungs to become thick mucus
• Proteins must be delivered INSIDE cells
• First disable a suitable virus – cold virus
• Carry in needed protein pump
• Works for a few weeks so far in clinical trials
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Using Biotechnology to Cure Severe
Combined Immune Deficiency
• New cells come from stem cells (more in Ch 25)
• Childhood immunodeficiency – SCID = severe
combined immune deficiency
• Most die before 1st birthday
• 1 in 80,000 children
• Remove stem cells from bone marrow
• Treat with virus to add gene to create normal white
blood cells
• Two children treated developed leukemia
• Hopeful, but not here yet…
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What Are the Major Ethical
Issues of Biotechnology?
• Should Genetically Modified Organisms Be Permitted in
Agriculture?
–
–
–
–
Herbicide resistant foods can allow weed reduction (saves 10% of crop)
+ rice with more beta-carotein (makes vitamin A in the body0
Soybeans with more healthy oils etc.
Are Foods from GMOs Dangerous to Eat?
•
•
•
•
More of the same is not a hazard
Allergies? (StarLink contains Bt protein – not digested as easily)
2003 U.S. Society of Toxicology = no significant dangers
Benefit = more food, healthier comonents
– Are GMOs Hazardous to the Environment?
• Genes (resistance to herbicides for example) carried in pollen for miles
• Pollen won’t catch, but bacteria and viruses can carry segments!
• 2002 committee of the U.S. National Academy of Sciences pointed out that
such crops MAY pose a threat to the environment
• Animals not as much of a threat except for fish…what will eventually get to
the oceans/ hydrologic systems
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Should the Human Genome Be
Changed by Biotechnology?
• Test a child and decide to abort it?
• Ethical?
• How about engineering size, strength, eye,hair,
skin color?
• Serious issues for the future…
• Human cloning technology might allow
permanent correction of genetic defects (p.
209)
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parents with genetic disease
fertilized egg with
defective gene
embryo with
genetic defect
baby with
genetic disorder
therapeutic
gene
treated culture
disabled virus
egg cell
without
nucleus
genetically corrected
cell from culture
genetically corrected
egg cell
genetically corrected
clone of original embryo
healthy baby
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