Transcript Non-Mendelian Genetics

Do Now :What is the probability
that a heterozygous cross will
produce homozygous recessive
offspring?
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Some traits don’t follow the simple
dominant/recessive rules that Mendel first
applied to genetics.
Traits can be controlled by more than one
gene.
Some alleles are neither dominant nor
recessive.
One allele is not completely dominant over
another.
 The heterozygous phenotype is a blending
of the two homozygous phenotypes.
Example: four o’clock flowers
 rr=red
 ww=white
 rw=pink (blending of the two alleles)
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Two alleles are both
expressed as a
dominant phenotype
Coat color in cows
 RR: Red
 WW: White
 RW: Roan, white with
red spots (NOT pink!)
Codominance
More than two choices of alleles are present for a
trait
 ABO blood type has three alleles
 ABO Blood types:
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 If both A and B are present, type is AB
 Neither is recessive
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Individuals can be type A, B, AB, or O (recessive)
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The transfusion will work if a person who is going
to receive blood has a blood group that doesn't
have any antibodies against the donor blood's
antigens.
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People with blood group 0 are called
"universal donors" and people with blood
group AB are called "universal receivers."
When several genes affect a character, it is called
a polygenic character.
 eye color is affected by several genes. One gene
controls the relative amount of greenness of the
eye, and another gene controls brownness. (The
recessive condition in both cases is blue eyes.)
 Other genes also affect eye color.
 Other examples of polygenic characters in humans
are height and skin color. In fact, most characters
are polygenic.
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Phenotype can be affected by conditions
in the environment, such
as nutrients and temperature.
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Males have an X and a Y
chromosome
Females have two X
chromosomes
These chromosomes determine
sex, so genes located on these
chromosomes are known as sexlinked genes.
The X chromosome is much
larger than the Y, so it
carries more genes than
the Y chromosome.
•Disorders that are sex-linked are much
more common in males, because they
would only need 1 recessive allele to have
the trait; rather than the two recessive
alleles the females need.
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Recessive trait
Disorder where individuals are missing the
normal blood clotting protein.
Uncontrolled bleeds from minor cuts or
bruises.
Female genotype: XhXh (with disease)
XHXh ( carrier)
Male genotype: XhY
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Recessive
Inability to see certain colors
Female genotype: XbXb –colorblind
XbXB - carrier
Male genotype: XbY- colorblind
Calico is a coat color found in cats, which is caused
by a SEX-LINKED, CODOMINANT allele.
 B = Black
R = Orange
BR = Calico
 The following genotypes are possible;
 Female cats can be black XBXB, orange XRXR, or
calico XBXR
Male cats can be black XBY or orange XRY
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Show each of the crosses below and include
the phenotypic ratios of the offspring.
1. A black male crossed with an orange
female
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2. An orange male crossed with a calico
female
A woman who is heterozygous for normal
vision marries a man who is colorblind. What
are the chances of them having a son or
daughter who is colorblind?
**NOTE: You have to use X’s and Y’s, and
read the Punnett square separately for
boys and girls!**
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A woman who is homozygous for normal
blood clotting marries a man who has
hemophilia. What are the chances of them
having a son or daughter with hemophilia?