Chapter 13 - Angelfire

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Transcript Chapter 13 - Angelfire

Chapter 13
Genetic Technology
Selective Breeding
• For a long time, humans have selected the
best plants and animals to
• Why?
• Examples?
• Milk Cows
– 1947 - produced 4,997 lbs... of milk/year
– 1997 - produced 16,915 lbs.... of milk/year
• Increasing the frequency of desired alleles
in a population is the essence of genetic
• Mating between closely
related individuals
• Why?
• Done to make sure that
breeds consistently exhibit a
trait and to eliminate
undesired trait
– Creates purebred lines
• Can be bad also
– Can bring out harmful,
recessive alleles in a “family”
• It can be beneficial to
create hybrids
• For example, diseaseresistant plants crossed
with plants that produce
bigger fruit
– Offspring get both qualities
• Hybrids produced by
crossing two purebred
plants are often larger and
stronger than their parents
Test Crosses
• A test cross is a cross of an
individual of unknown
genotype with an
individual of known
genotype (usually
homozygous recessive)
• How will this work?
– Results when heterozygous
x homozygous?
– Results when homozygous
x homozygous?
• When is this practical?
Section 1 Review
• A test cross made with a cat that may be heterozygous for a
recessive trait produces ten kittens, none of which has the
trait. What is the presumed genotype of the cat? Explain.
• Suppose you want to produce a plant that has red flowers
and speckled leaves. You have two offspring, each having
one of the desired traits. How would you proceed?
• Why is inbreeding rarely a problem among animals in the
• Hybrid corn is produced that is resistant to bacterial
infection and is highly productive. What might have been
the phenotypes of its two parents?
• How is selective breeding done?
• What effect might selective breeding of plants and animals
have on the size of Earth’s human population? Why?
Genetic Engineering
• Selective breeding may take a while to
produce a purebred “line”
• Genetic engineering is a faster and more
reliable method for increasing the
frequency of an allele in a population
• This involves cutting - or cleaving DNA from one organism into small
fragments and inserting the fragments
into a host organism of the same or a
different species
• Also called recombinant DNA
– Connecting, or recombining,
fragment of DNA from different
Transgenic Organisms
• Plants and animals that contain functional recombinant DNA from
an organism of a different genus
– Ex: they grow a tobacco plant that glows from a gene in a firefly
• 3 steps:
– Isolate the foreign DNA fragment to be inserted
– Attach the DNA fragment to the carrier
– Transfer the DNA into the host organism
Restriction Enzymes
• Bacterial proteins that have the ability to cut
both strands of the DNA molecule at a
specific nucleotide sequence
• Some enzymes cut straight across
– Called blunt ends
Restriction Enzymes
• Many enzyme cut in palindromes
– Ex: a protein only cuts at AATT, it will cut the two
fragments at different points - not across from each
other (called sticky ends)
• Called sticky ends because they want to bond with things
due to their “open” end
• These sticky ends are
beneficial, because if the
same enzyme is used in
both organisms, they will
have identical ends and
will bond with each other
• DNA fragments don’t just attach themselves to another
fragment, they need a carrier
– A vector is the means by which DNA from another
species can be carried into the host cell
• Vectors may be biological or mechanical
• Biological vectors include viruses and plasmids
– A plasmid is a small ring of DNA found in a bacterial
• Mechanical vectors include micropipettes
and a little metal bullet coated with DNA
shot with a gene gun into a cell
Insertion Into a
• If the plasmid and the
DNA fragment were
both cleaved with the
same enzyme, they
will stick together
because they have
“sticky ends”
• A second enzyme
helps this process
• Mini-Lab 13.1
– Page 343
• Modeling Recombinant DNA
– Page 354
Gene Cloning
• Once the fragment is in the
plasmid, the bacterial
makes many copies of the
– Up to 500 copies per
• Clones are genetically
identical copies
• Each copied recombinant
DNA molecule is a clone
• If the plasmid is placed
into a plant or animal cell,
the cell reproduces that
DNA also and makes those
proteins coded for
Cloning Animals
• Dolly was the first animal cloned in 1997
• Since then, goats, mice, cattle, pigs, etc.
have been cloned
• Take DNA out of embryonic stem cells or
zygote and insert new DNA
Polymerase Chain Reaction
• A way to artificially replicate DNA
• DNA is heated and the strands separate
• An enzyme isolated from a heat-loving
bacterium is used to replicate the DNA
when nucleotides are added (in a
– Makes millions of copies in less than a day
• Why could this be helpful?
Sequencing DNA
• First, PCR is done to make millions of copies
• Separate the strands of DNA
• Place in four different tubes with four different restriction
enzymes that cut at one of the four bases (A,T,C,G)
– A fluorescent tag is also placed at each cut
• The fragments are separated according to size by a process
called gel electrophoresis
– Produces a pattern of
fluorescent bands in
the gel
• Shows the sequence of
Gel Electrophoresis
• The gel is like firm gelatin
– Molded with small wells at one end
– Has small holes in the gel (not visible)
• DNA has a slight negative charge
• A current is run through the gel and an
added buffer fluid
– DNA will move towards the positive end
• Smaller fragments fit through the holes in
the gel better and move farther
Gel Electrophoresis
Gel Electrophoresis Lab
Recombinant DNA in Industry
• E. coli has been modified to produce an
indigo dye to color blue jeans
• Recombinant DNA has been used to help
production of cheese, laundry detergent,
paper production, sewage treatment
– Increase enzyme activity, stability and
Recombinant DNA in Medicine
• Production of Human
Growth Hormone to treat
pituitary dwarfism
• Insulin Production by
bacterial plasmids
• Antibodies, hormones,
vaccines, enzymes, and
hopefully more in the
Transgenic Animals
• Mice reproduce quickly and have
chromosomes that are similar to humans’
• The genome is known better
• The roundworm Caenorhabditis elegans
and the fruit fly, Drosophila melanogaster
are also well understood
– Used in transgenic studies
Transgenic Animals
• A transgenic sheep was produced that
contained the corrected human gene for
• This human gene inserted into the sheep
produces the clotting protein in the sheep’s
– This protein can then be given to hemophilia
Recombinant DNA in Agriculture
• Crops that stay fresh longer and are more
resistant to disease
• Plants resistant to herbicide so weeds can be
killed easier
• Higher product yields or higher in vitamins
• Peanuts and soybeans that don’t cause
allergic reactions
Section 2 Review
• How are transgenic organisms different from
natural organisms of the same species?
• How are sticky ends important in making
recombinant DNA?
• How does gel electrophoresis separate fragments
of DNA?
• What is a restriction enzyme?
• What is PCR?
• Explain two ways in which recombinant bacteria
are used for human applications.
• Many scientists consider engineering to be simply
an efficient method of selective breeding. Explain.
The Human Genome
• In 1990, scientists in the U.S.
organized the Human Genome Project
– An international effort to
completely map and sequence the
human genome
• Approximately 20,000 - 25,000 genes
on 46 chromosomes
• In February, 2001, the PGP published
its working draft of the 3 billion base
pairs in most human cells
• Mini-lab, page 350 (as a class)
Linkage Maps
• Crossing over occurs
• Geneticists use the
frequency of
crossing over to map
the relative position
of genes on a
– Genes that are further
apart are more likely
to have crossing over
Linkage Mapping
• Suppose there are 4 genes on a chromosome – A, B,
C, D
• Frequencies of recombination as follows:
Between A & B: 50% (50 map units)
Between A & D: 10% (10 map units)
Between B & C: 5% (5 map units)
Between C & D: 35% (35 map units)
• These give a relative distance between genes
• A -10 units- D -35units- C -5 units- B (whole thing
is 50 units)
Linkage Mapping
• The problem with this in humans, is that we
have relatively few offspring
• Geneticists mark genes that have specific
• They can follow these through inheritance
and hopefully see what it does
– If a gene is marked, not passed on and that trait
doesn’t show up, it may help identify the gene
Sequencing the
Human Genome
• Genome is cloned,
cut into segments,
and then run through
gel electrophoresis
• Arrange the
fragments and get a
• Machines can do
this much faster
Applications of HGP
• Probably the biggest application so far has
been the identification of genetic disorders
• Often done prenatal
– Take cells from
amniotic fluid and
look for deviations
Gene Therapy
• The insertion of normal genes into human
cells to correct genetic disorders
• Have been used for SCID (severe combined
immunodeficiency syndrome), cystic
fibrosis, sickle-cell anemia, hemophilia and
• Scientists are hopeful his will help treat
cancer, heart disease, AIDS and many other
DNA Fingerprinting
• Genes are separated by segments of
noncoding DNA (“junk DNA”)
– These segments produce distinct combinations
of patterns unique to each individual
• What are the uses?
DNA Fingerprinting
• Small DNA sample
• Clone samples with PCR
• Cut into fragments
• Separated by gel
• Chances of two identical
matches are infinitesimally
Stem Cells
• An undifferentiated cell
– Doesn’t have a specific function yet
• Will eventually become differentiated
– It will get a specific function and then can only
do certain thins
• GSLC site
Other Uses of DNA Technology
Look at mummies to understand them
Looked at Abraham Lincoln’s hair
Look at fossils and compare extinct species
They now seem unlimited.
Is that a good thing?
Section 3 Review
• What is the Human Genome Project?
• Compare a linkage map and a sequencing
• What is the goal of gene therapy?
• Explain why DNA fingerprinting can be
used as evidence in law enforcement.
• Describe some possible benefits of the
Human Genome Project