Download Chapter 7 and Chapter 8

Genetics
The connection between
Gene expression and Genetics
• Genotype is the genetic make up of an organism (gene),
which codes for a protein.
The protein has a specific function which produces a trait.
• Phenotype is the appearance of an organism (trait)
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Closer look at Genotype:
the combination of alleles an individual carries
Genes that show complete dominance
The type of inheritance in which both
heterozygote and dominant homozygote
have the same phenotype.
Genotypes
AA homozygous dominant
Aa heterozygous
aa homozygous recessive
Phenotypes
dominant
dominant
recessive
3 genotypes
2 phenotypes
How can two individuals with different genotypes for a particular
trait be identical in phenotype?
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Determine your partner’s phenotype and possible genotype
Traits
Earlobes: detached is dominant over attached
E
e
Tongue:
tongue rolling is dominant over not being able to roll tongue
T
Hair line:
t
widow’s peak is dominant over straight hairline
W
w
How are these traits (alleles) inherited?
What happens to alleles during meiosis?
What happens to alleles after fertilization?
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What happens to the alleles during meiosis?
• During meiosis,
If we look at one gene only:
A gamete has only one allele
• How many types of gametes
does each genotype produce?
• Homozygous individual
produces only one kind of
gametes
• Heterozygous individual
produces two kinds of gametes
Genetics in Class
Practice # 1
In peas, the allele for purple flowers (P) is dominant
to the allele for white flowers (p).
What gametes would be produced by
a plant that has white flowers?
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What happens during fertilization?
Fertilization creates allele pairs again in the offspring
Gamete types
Parent 1:
Genotype Aa
R
Offspring:
Genotype rr
r
R
Parent 2:
Genotype Aa
During fertilization
r
Chance determines
which alleles
the offspring receives
from each parent
Punnett square shows all the possible
offsprings from a matting
1. Write down the alleles, and all
genotypes and phenotypes as reference
X
2. Determine the possible genotypes of
the parents
3. draw a p-square
4. "split" the letters of the genotype for
each parent & put them "outside" the psquare
5. determine the possible genotypes of
the offspring by filling in the p-square
6. estimate probabilities for
genotypes & phenotypes of offspring
7. bask in the glow of your
accomplishment!
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Practice # 2
Assume tall (T) is dominant to dwarf (t).
If a homozygous dominant individual is crossed
with a dwarf.
What will the offspring look like?
Fill in the blanks:
allele, recessive, homozygous, dominant, chromosomes
b)
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A gene with Incomplete Dominance results in
in the heterozygous individual expressing
an intermediate phenotype
EXAMPLE: gene for color of flowers
Genotypes
RR
rr
Rr
Phenotypes
3 genotypes and 3 phenotypes
3rd phenotype is an intermediate
of the recessive and dominant
Practice # 4
Flower color in snapdragons
is an example of incomplete dominance.
If a pink-flowered plant is crossed with a pink-flowered plant,
What will the progeny of plants look like?
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A gene with Codominance results in
in a heterozygous individual expressing
both recessive AND dominant phenotypes
EXAMPLE: gene for color of hair in dogs
Genotypes
Phenotypes
AOB blood type
AOB blood gene codes for
the type of antigen found
in the membrane of red blood cells
AOB blood gene is a codominant gene
AOB blood gene has more than two alleles (multiple alleles) Alleles: IA
Genotypes
Phenotypes
IB
i
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Practice # 5
A man who has type B blood
And
a woman who has type A blood
have a child with type O blood.
How is this possible?
Sex chromosomes determine sex in many species
In some cultures,
The mother is blamed for not bearing a boy,
is this justified?
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Genes carried in the sex chromosomes
exhibit a unique pattern of inheritance
• Some genes are present on the X-chromosome but missing on the shorter
Y-chromosome.
• In the non-homologous region of the X-chromosome a male will only have
one allele for any gene in this region.
Hemophilia is a X-linked recessive disease
Possible alleles
XH
Xh
Y
Possible genotypes and
phenotypes
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Solving genetic problems for X linked genes
Problem should state that
it is a sex linked gene
Allele is attached to the X chromosome
Need to determine gender of offspring
In order to determine phenotype
Color blindness is a recessive trait
Practice # 6
A couple are both normal,
but their son suffers from hemophilia.
What fraction of the couple’s children
are likely to suffer from hemophilia?
What fraction are likely to be carries?
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Pedigrees are often used to determine the mode of
inheritance (dominant, recessive, etc.)
of genetic diseases.
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