Transcript 4.1 Genetics

Bellringer:
Where did you get your 46
chromosomes from that you have
in each of your cells?
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UNIT 4 PART 1: MODERN
GENETICS
• In sexual reproduction
the new individual
develops from the
zygote formed by the
union of two gametes,
one from each parent.
• Because hereditary
material comes from
two different parents,
the offspring is both
similar to, and different
from, each parent.
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• GENETICS is the branch of biology that studies
the ways in which hereditary information is
passed on from parents to offspring.
• Gregor Mendel, an Austrian monk, was the first
to scientifically study heredity in the 1800s. He
studied the inheritance of certain traits in peas
using 1000’s of pea plants.
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• Mendel then thought that each trait was
controlled by a pair of “factors”, and that
each factor could be one of two kinds. For
example, one factor for green pod color
and one for yellow pod color.
• In a cross, the offspring receives one
factor from each parent.
• In a hybrid one factor may be hidden, but
show itself again in later generations when
fertilization brings together two of these
recessive factors. Ex: yellow pod color
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• When more was
learned about cells, it
was noted that the
movements of the
chromosomes during
meiosis and
fertilization would
account for the
separation and
recombination of
Mendel’s factors, so it
was thought that the
chromosomes might
carry the factors.
• The factors were then
called genes.
THE GENECHROMOSOME
THEORY
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ALLELES
• It is now known that genes do carry the
hereditary information, and that they are
on chromosomes in a definite order.
• Each body cell has two copies of the gene
for each trait. These two copies can be the
same or different.
• Each form of a gene that controls a trait is
called an allele. Pea pod color has two
alleles: green and yellow.
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• If the two alleles an organism has for a trait
are the same, like GG, then the individual is
said to be homozygous for that trait. If the
alleles are different, Gg, the individual is said
to be heterozygous.
• The genetic makeup of an individual, the
alleles it has, is called its genotype. The way
the individual looks as a result of its
genotype, its physical trait, is called its
phenotype.
GG = green; Gg = green; gg = yellow
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SEX DETERMINATION
• Scientists noticed that all
the chromosome pairs
were the same in both
males and females except
for one pair.
• This pair determines the sex of the individual.
These are the sex chromosomes. The other
pairs are called autosomes.
• In fruit flies, as well as humans, the two sex
chromosomes look the same in the female
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(XX), but are different in the male (XY).
GENE
• The traits Mendel
studied were all on
different chromosomes.
• Most chromosomes
have 100’s of genes so
many are inherited
together.
• Genes on the same
chromosome are said
to be Linked.
• abcde are linked, so
are ABCDE.
LINKAGE
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LINKED TRAITS
• Linked genes are
inherited together.
• Ex:
– Blonde hair & Blue
eyes
– Red hair & Freckles
– White cats & deafness
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CROSSING OVER
• Linked traits may be
separated by crossingover of homologous
chromosomes.
• Genes A an a have
crossed over and
formed new linkage
groups:
– Abcde and aBCDE
• Ex:
– Brown hair & Blue eyes
– Red hair & dark skin
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• Genes determine the
characteristics of an
individual and are carried
on chromosomes.
• It still needed to be
known what a gene was
and how it worked.
• Through a number of
experiments it was
determined that
chromosomes were made
of DNA and that DNA
was the hereditary
material.
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DNA STRUCTURE
•
•
A DNA molecule is made up
of thousands of subunits
called nucleotides.
Each nucleotide has three
parts:
1. phosphate group
2. five carbon sugar –
deoxyribose
3. nitrogenous base
• 4 kinds of bases: adenine
(A), guanine (G), cytosine
(C), and thymine (T)
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DNA STRUCTURE
•
•
•
Watson and Crick
discovered the shape
of DNA.
Two chains of sugarphosphate groups
running parallel to
each other with pairs
of bases joining the
chains like rungs of a
ladder.
Twisting this ladder
forms the double
helix.
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DNA STRUCTURE
• Every DNA molecule has a different
sequence of bases.
• The order of bases along one strand of
the double helix determines the
matching bases on the other side:
– A always pairs with T; C always with G
– So if one strand is AGGTAC the other will
be:
TCCATG
• The two strands are said to be
complementary.
• One gene = a sequence of hundreds of
bases.
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DNA REPLICATION
• DNA can make
copies of itself.
• The two strands unzip
at the weak bonds
between the bases.
• Two new molecules
are built by attaching
new nucleotides to
each original strand
which acts as a
template, or pattern.
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DNA REPLICATION
• Each “new” strand will
actually be half old
and half new.
• The copies of the
DNA molecule can be
passed on to the
daughter cells during
cell division.
• This is how the
chromosomes
replicate.
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DNA FUNCTION
• How do the genes
control all body
traits and
functions?
• One Gene  One
Polypeptide
– Each gene codes
for the production
of a different
polypeptide chain.
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• The work of the cell is carried out by the
proteins it assembles.
• Proteins are made up of chains of
amino acids –i.e. polypeptide chains.
• There are 20 different types of amino
acids.
• The sequence of amino acids
determines the protein created and the
shape it takes on.
• Examples of proteins include: enzymes,
hormones, and structural proteins.
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Bellringer
• The diagram below
represents a microscopic
structure observed during
mitosis. The region
indicated by letter A is
known as
• (1) an enzyme
• (2) a gamete
• (3) a gene
• (4) an amino acid
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Bellringer 2/22
• The inability of an organism to
produce certain proteins can occur
when an organism is lacking an
enzyme needed to combine
• (1) oxygen molecules
• (2) simple sugars
• (3) amino acids
• (4) biological catalysts
PROTEIN SYNTHESIS BASICS
• One gene makes one polypeptide.
• The order of bases of three adjacent
nucleotides codes for a particular amino
acid. These 3 bases are called a codon.
– e.g. CAG is the DNA codon for glutamine
–
AAA is the DNA codon for phenylalanine
• Some codons indicate where a
polypeptide begins or ends. (Similar to
punctuation in a sentence.)
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•
•
•
Protein Synthesis Helper:
RNA
Polypeptides are synthesized
outside the nucleus, but the
genes are inside the nucleus.
RNA transcribes the genes
from DNA & takes them to
ribosomes outside the nucleus.
RNA is similar to DNA, but it
has 3 main differences:
1. the sugar is ribose
2. Uracil (U) takes the place
of the Thymine (T) base
3. RNA is single stranded
RNA
DNA
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THREE TYPES OF RNA
Messenger
(mRNA)
Transfer
(tRNA)
Ribosomal
(rRNA)
copies the
carries the
genetic code for a instructions
protein from DNA outside the
nucleus
carries amino
Amino acid is
acids to
attached to chain if
ribosomes
anticodon pairs
with codon
in the nucleoli,
site of the
protein and rRNA assembly line in
join together to
the cytoplasm of
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form a ribosome all cells
Summary of Protein Synthesis
• mRNA copies a gene (transcription)
Translation:
• mRNA attaches to
a ribosome
• tRNA brings amino
acids to the ribosome,
base pairing its
anticodon to the
mRNA codon
• Amino acids connect
to each other
• When finished, a
polypeptide is released
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INSIDE THE
NUCLEUS
OUTSIDE THE
NUCLEUS
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Transcription & Translation Practice
TAC CGG ACA GTG TAA TTC CAG TCA ATT
(DNA)
GCC UGU
AUG
AGU UAA
____ ____
___ CAC
____ AUU
____ AAG
___ GUC
____ ____
___
(RNA)
Lys ____
Ser (Stop)
Met ____
Ala Cys
Ile ___
His ____
Val ____
____
___ ____
___
(Amino Acid)
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Bellringer 2/23
• DNA is able to control cellular
activities most directly by regulating
the process of
(1) meiotic division
(2) protein synthesis
(3) active transport
(4) selective breeding
GENE EXPRESSION
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All your body cells originated from a single
cell, so they all contain the same genes.
However, each cell only turns on the
genes it needs; it uses only some of the
genetic material it contains.
This is called expression.
Expression causes differentiation- the
formation of special types of cells.
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DIFFERENTIATION
• Chemical signals from
within the cell or from
other cells may
activate certain
genes. Ex: hormones
• The proteins that are
assembled in each
type of cell are
different so the cells
themselves become
different.
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GENE EXPRESSION CAN BE
AFFECTED BY THE ENVIRONMENT
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The Himalayan rabbit is
white with some black
fur on some cooler
parts. If the skin on the
back is shaved & an ice
pack applied, the new
fur will also be black.
Alligators’ sex is determined by the egg temp.:
>34oC for males, <30oC
for females.
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A hydrangea plant has blue flowers when grown in acidic soil,
but has pink flowers when grown in basic soil. A clone of the
pink-flowered plant is grown in acidic soil and produces blue
flowers. This change in flower color is most likely due to
(1) sexual reproduction in the plants, resulting in variation
(2) asexual reproduction in the plants, resulting in variation
(3) genes being expressed in different ways due to
environmental conditions
(4) a gene mutation that occurred after the clone was produced
• Which organic compounds would be
the best to analyze in order to
determine if two species are closely
related?
• (1) fats
• (2) starches
• (3) sugars
• (4) proteins
Even though human proteins are synthesized from only
20 different amino acids, there are thousands of
different proteins found in human cells. This great
variety of proteins is possible because the
1)Size of a specific amino acid can vary within a protein
2)Chemical composition of a specific amino acid can
vary
3)Sequence and number of amino acids can be different
in each protein
4)Same amino acid can have many different properties
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