Download 1. Genetics overview - Winston Knoll Collegiate

Chapter 11
11-1 What is genetics?
The scientific
study of
heredity
Gregor Mendel
Born in 1822 in
Czechoslovakia.
Became a monk at a
monastery in 1843.
Taught biology and
had interests in
statistics.
Also studied at the
University of Vienna
Mendel continued
Between 1856 and
1863 he grew and
tested over 28,000
pea plants
Mendel’s Peas
Easy to grow.
Easily identifiable traits
Can work with large numbers of
samples
Mendel’s experiments
The first thing Mendel did was create a
“pure” generation or true-breeding
generation.
He made sure that certain pea plants
were only able to self pollinate,
eliminating unwanted traits.
He did this by cutting away the stamen,
or male part of each flower
Genes and dominance
Trait : a characteristic
Mendel studied seven of these traits
After Mendel ensured that his truebreeding generation was pure, he then
crossed plants showing contrasting
traits.
He called the offspring the F1
generation or first filial.
What will happen when pure
yellow peas are crossed with
pure green peas?
All of the
offspring were
yellow.
Hybrids = the
offspring of
crosses between
parents with
contrasting traits
What did Mendel
conclude?
Inheritance is determined by factors
passed on from one generation to
another.
Mendel knew nothing about
chromosomes, genes, or DNA. Why?
These terms hadn’t yet been defined.
What were Mendel’s
“factors”
The ‘factors” that Mendel mentioned
were the genes.
Each gene has different forms called
alleles
Mendel’s second principle stated that
some alleles are dominant and some
are recessive.
Mendel’s second cross
He allowed the F1 generation to selfpollinate thus producing the F2
generation.
Did the recessive allele completely
disappear?
What happened when he crossed two
yellow pea hybrid (F1) plants?
Results:
¾ of the peas were yellow, ¼ of
the peas were green.
During the formation of the sex cells or
gametes, the alleles separated or
segregated to different gametes. (pollen
and egg)
11-2 Probability
The likelihood of a
particular event
occurring. Chance
Can be expressed
as a fraction or a
percent.
Example: coin flip.
Punnett Square
Developed by
Reginald Punnett.
A diagram used to
show the probability
or chances of a
certain trait being
passed from one
generation to
another.
Reading Punnett
squares
Gametes are placed above and to the
left of the square
Offspring are placed in the square.
Capital letters (Y) represent dominant
alleles.
Lower case letters (y) represent
recessive alleles.
Punnett square example
Homozygous = when an organism
possesses two identical alleles. ex.

YY or yy
Heterozygous = when an organism
possesses different alleles. ex.

Yy
Phenotype vs genotype
Genotype
 The genetic makeup
 Symbolized with
letters
 Tt or TT
Phenotype
Physical
appearance of the
organism
Expression of the
trait
Short, tall, yellow,
smooth, etc.
Probability and
statistics
No one event has a greater chance of
occurring than another.
You cannot predict the precise outcome
of an individual event.
The more trials performed, the closer
the actual results to the expected
outcomes.
Punnett square review:
11-3 Independent
Assortment
The two factor cross. Example: color
and shape of peas.
F1 cross to produce the F2 generation
Ex RRYY x rryy
Round yellow mated with wrinkled green
• Offspring would all be hybrid for both
traits (RrYy)
What is independent
assortment?
Alleles
separate
independently
during the
formation of
gametes.
The dihybrid cross
Punnett square on board:
Some exceptions to
Mendel’s principles:
Some alleles are neither
dominant nor recessive.
Many traits are controlled by
more than one gene (polygenic
traits)
Incomplete dominance
A situation in which neither allele is
dominant.
When both alleles are present a “new”
phenotype appears that is a blend of
each allele.
Alleles will be represented by capital
letters only.
Japanese four-o-clock
flowers
Red flower plant genotype = RR
White flower plant genotype = WW
Pink flower plant genotype = RW
What happens when a
red flower is crossed
with a white flower?
According to
Mendel either
some white and
some red or all
offspring either
red or white.
All are pink
Codominance
When two alleles both appear in the
phenotype.
Usually signified using superscripts.
example: color of hair coat in cattle.
crcr = red hairs
cwcw = white hairs
crcw = roan coat (mixture of both colors)
Roan cattle inheritance
Multiple allele inheritance –
Blood Types
When two or more alleles contribute to
the phenotype.
Human blood types: A,B,O and AB
A and B are codominant to each other.
Both A and B are dominant over O.
Human Blood types:
Type A
TYPE A
Allele = IA
Blood cells
have small
antigens on the
surface.
Human Blood types:
Type B
TYPE B
Allele = IB
Cells coated
with type B
antigens
Human Blood types:
Type AB
TYPE AB
genotype = IAIB
Blood cells
contain both
types of antigens
Known as
universal recipient
Human Blood types:
Type O
TYPE O
Allele = i
No antigens on
the surface of
the blood cells
Known as
universal donor
6 different genotypes
IAIA
IAIB
IBIB
IBi
IAi
ii
Type A
Type AB
Type B
Type B
Type A
Type O
How common are the
different blood types?
Sample Problem:
A man with type AB blood
marries a woman with type B
blood whose father has type O
blood. What are the chances
that they have a child with type
A blood? Type AB?
Polygenic traits
Traits controlled by two or more
genes.
Examples:
 Human height,
eye and skin
color
11-4 Meiosis
A method of cell division similar to
mitosis.
2 main differences:
1. There are two divisions to produce 4
daughter cells
2. The cells produce contain ½ the
chromosomes as the original cell
Chromosome number
All cells of an
organism contain a
specific number of
chromosomes.
Most cells are
diploid (2n) meaning
they have two
copies of each
chromosome
Events of Meiosis I
During prophase I, each
chromosome pairs with its
homologous chromosome to
form a tetrad
Crossing-Over
Crossing-over: an
exchange of
genetic material
between sister
chromatids
Results in greater
variation
Meiosis II
Neither cell replicates its chromosomes.
Each cell splits (similar to mitosis)
Produces four daughter cells.
Animation
Gametogenesis
Literally
means
“creation of
gametes”
Egg and
sperm
2 types: Spermatogeneis
& Oogenesis
Net result:
Spermatogensis
4 mature sperm
Each sperm has
exactly half the
number of
chromosomes as
the father.
Oogensis
1 mature ova or
egg.
Each egg has
exactly half the
number of
chromosomes as
the mother.
11-5 Gene Linkage
Are genes “linked” to each other on
chromosomes?
Morgan found that many genes are
linked together.
It was determined that chromosomes,
not genes, assort independently during
meiosis.
Gene Maps
First developed
by Sturtevant in
1911.
The farther apart
two genes are,
the more likely
they will be
separated in
meiosis.
Transcription – Translation
to Protein Synthesis
Transcription – overview
Genetic Code = triplets in DNA=the amino
acids in proteins
There are twenty different amino acids that
build proteins
There are 64 different triplets/codons
Each amino acid is coded for by more than
one triplet/codon
Translation-Overview
The Players
mRNA:messenger RNA
- carries protein recipe from the nucleus
tRNA: transfer RNA
-brings amino acids to the ribosome
Ribosome: the site of protein synthesis
- made of rRNA (ribosomal RNA ) and Protein
The Process of Translation
mRNA takes recipe to the ribosome in
cytoplasm
ribosome attaches to the mRNA
Translation
The ribosome moves along the mRNA until it
reaches the “Start” codon
Start codon = AUG signals the start of the
recipe
AUG also codes for the amino acid methionine
The process of Translation
•A molecule of transfer RNA brings the amino acid called
for by the mRNA to the ribosome
•transfer RNA = tRNA
The process of Translation
A second tRNA brings the second amino acid to the
ribosome
The amino acids are joined together to begin the protein
THE PROCESS OF TRANSLATION CONCLUDED
The ribosome moves over 1 codon and
another tRNA molecule brings another amino
acid
The process continues until the stop codon
on the mRNA is reached
-the stop codon = the end of the
protein recipe
Meet tRNA
each molecule of tRNA carries a specific
type of amino acid
- each tRNA molecule can only carry one
type of
amino acid
The tRNA has a group of 3 nucleotides
at the base called the anticodon
How does tRNA know which amino acid
goes where?
The anticodon on tRNA is complementary to a mRNA codon
the amino acid that a tRNA molecule carries is the amino acid that the
complementary mRNA codon codes for
Example:
mRNA codon = GAC = aspartic acid
tRNA anticodon = CUG carries only aspartic acid
What’s
What?
Making the
building(protein)