Transcript Non-Mendelian Genetics

Non-Mendelian
Genetics:
Genes that don’t
obey Mendel’s
laws
2 Types of Human Chromosomes
1.
Autosomes- Contain genes that code for
traits unrelated to the sex of the individual.
Somatic cells (non-sex cells) have 22 pairs
(44) of these.
• All of the genes studied thus far have been
on autosomes.
2. Sex Chromosomes- Contain genes that code
for the sex of the individual as well as other
traits. Somatic cells have 1 pair (2) of these.
•
Male- XY
•
Female- XX
Determining Sex
X
X
MOM
X
X X
X X
X Y
X Y
DAD
Y
Sex-Linked Traits
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X-linked disorders include Hemophilia (bleeding
disease) and color-blindness. These are both
recessive traits.
Males have 1 x sex chromosome; therefore, it only
takes that one x to be affected to make the male
have a x-linked disease
X-linked disorders show up rarely in females
because both of the x sex chromosomes must be
recessive.
Y-linked disorders include male baldness and
some forms of infertility.
Females cannot have Y-linked disorders.
Click and choose the
button
Colorblindness Tests
Sex-linked Punnett Square Problems
1. Hemophilia is a recessive trait linked to
the x sex chromosome. What are the
genotypic/phenotypic ratios of a cross
between a carrier female and a normal
male?
2. Red-green colorblindness is a recessive trait
linked to the x sex chromosome. A red-green
colorblind female and a normal male have a child.
What is the probability (regardless of gender) that
it will be red-green colorblind?
3. Muscular Dystrophy is a X-linked recessive
trait. A carrier female and a normal male have
children. Will any of their children have a
chance of having this disorder? If so, list the
proportion(s), including the gender(s).
4. A woman has a brother with Hemophilia and a
mother and father who are normal. What is the
probability that this woman is a carrier if she is
normal?
Incomplete Dominance
- This is when neither form of the gene is able
to mask the other. Instead, they
phenotypically blend together.
- An example of this is snapdragon petal color:
- R1R1 – RED
- R2R2 - WHITE
- R1R2 – PINK
In a plant species, if the B1 allele (blue flowers)
and the B2 allele (white flowers) are incompletely
dominant (B1B2 is light blue), what offspring ratio
is expected in a cross between a blue-flowered
plant and a white-flowered plant?
Using the information from the previous
question, what would be the phenotypic ratio
of the flowers produced by a cross between
two light blue flowers?
Oompas can have red (H1H1), blue (H2H2), or purple
hair (H1H2). The allele that controls this is
incompletely dominant. A purple haired Oompa
marries a blue haired Oompa. What are the
phenotypic and genotypic ratios of their offspring?
Codominance
• Neither allele is dominant and both alleles
show up individually in the phenotype.
• Ex. Cat color
• TT– Tan
• TB – Tabby (black and tan spotted)
• BB - Black
Cattle can be red (RR = all red hairs), white
(WW = all white hairs), or roan (RW = red &
white hairs together.
a. Predict the phenotypic ratios of offspring when
a white cow is crossed with a roan bull.
b. What should the genotypes & phenotypes for
parent cattle be if a farmer wanted only cattle
with roan fur?
A cross between a black cat & a tan cat produces
a tabby pattern (black & tan fur together).
a. What is the phenotypic ratio of kittens if a tabby
cat is crossed with a black cat?
Multiple Alleles
• Some traits have more than 2 forms of the
gene.
• An example of this in humans is blood
type.
ABO blood groups
– Each individual is A, B, AB, or O phenotype
– A and B alleles are dominant to O.
– A and B alleles are codominant to each
other.
Blood Types
Blood Type:
• A
• B
• AB
• O
Genotype
• AA or AO
• BB or BO
• AB
• OO
If a male is homozygous for blood type B
and a female is heterozygous for blood
type A, what are the possible blood types
of the offspring?
Is it possible for a child with Type O blood
to be born to a mother who is type AB?
Why or why not?
A child is type AB. His biological mother is
also type AB. What are the possible
phenotypes of his biological father?
Rh Surface Protein
• In addition to the “A” and “B” proteins on
the surface of red blood cells, there is
another protein called “Rh”. It is called this
because it was first discovered in the
blood of the rhesus monkey.
• If a person’s red cells have the Rh protein,
then they are typed “positive”.
• If a person’s red cells lack the Rh protein,
then they are typed “negative”.
Identify the blood types
How is a person’s blood type
determined?
• When an incompatible blood type enters a
person’s body, the immune system
produces antibodies to fight the blood
cells. Antibodies bind to the A, B and/or
Rh proteins on the surface and cause the
blood to clump. This clumping is called
agglutination.
• Blood types are determined by mixing a
blood sample with antibodies to see if
clumping occurs.
A-Anti B-Anti Rh-Anti
Agglutination
Blood Type?
Incompatible Heart Transplant
Video
Gene Interactions
• Sometimes the expression of one gene
can affect the expression of other genes in
an organism.
• These interactions were not predicted by
Mendel’s Laws.
• Examples of this are epistasis and
pleiotropy.
Epistasis
• Epistasis is the interaction of two or more
genes to control a single phenotype.
• Usually 1 gene controls the expression of
another gene.
• Example: A labrador retriever’s coat color
is controlled by two alleles:
• A dominant allele “B” will produce
black pigment while the recessive
allele “b” produces brown pigment.
• The dominant allele “E” turns on the
“B” or “b” allele.
Labrador Retrievers
• BBEE, BBEe and BbEe --> Black retrievers
• bbEE and bbEe --> Brown retrievers
• BBee, Bbee, or bbee --> Golden retrievers
Epistasis Problem:
• What is the
phenotypic ratio if
you crossed two
labradors that are
heterozygous, BbEe,
for these two genes?
Epistasis Problem - Solution
Pleiotropy
• Expression of a single gene
which has multiple
phenotypic effects
• Marfan Syndrome – mutated
form of the gene for fibrillin.
• This gene can affect the
heart (aorta), height, chest
structure, flexibility of joints,
length of fingers, etc.
?
Environmental Influence on Phenotype
• The environment can affect an organism’s
phenotype.
• Examples:
– Soil acidity affects the color of hydrangea
flowers.
– Temperature affects the color of the fur in
Himalayan rabbits.
– Gender of clownfish is dependent on the “need”
for males/females for reproduction. They are
all born male but may become female if
necessary.
Human Genetics Test Review
Questions:
My daughter is type A, my grandson is type B.
What are the blood type(s) that the father
would have to be in order for my grandson to
be type B?
Red-green color blindness is X-linked in humans.
If a male is red-green color blind, and both
parents have normal color vision, which of
the male's grandparents is most likely to be
red-green color blind?
• A. maternal grandmother B. maternal
grandfather C. paternal grandmother
D.
paternal grandfather E. either grandfather is
equally likely
1. Suppose a child is of blood type A and the
mother is of type 0. What type or types may
the father belong to?
Suppose a father and mother claim they have
been given the wrong baby at the hospital.
Both parents are blood type A. The baby they
have been given is blood type O. What
evidence bearing on this case does this fact
have?
Hemophilia is a sex-linked recessive trait. Cross a
hemophiliac female with a normal male. Of all
their offspring, what is the probability they will
produce a hemophiliac daughter? (H = normal
blood, h = hemophilia)
A man with Type A blood marries a woman with
Type B blood. They have a type O child.
What is the probability of their 15th child
having type O blood?
A man whose father is type B and whose mother is
type A, has a blood type of A. He marries a
type A woman, whose parents had the same
blood types as his parents. What are the
genotypes of the man and the woman and what
is the probability that their first child will be
blood type A?
Coat color in cats is a codominant trait. Cats can be
black, yellow or calico. A calico cat has black and
yellow splotches. In order to be calico. the cat must
have an allele for the black color and an allele for
the yellow color. Show a cross between a calico cat
and a yellow cat. What are the possible genotypes
and phenotypes of the offspring?
A mother and father with normal color vision produce
six male children, two of whom exhibit red-green
colorblindness. Their five female children exhibit
normal color vision. Ignoring the fact that these
parents ought to seek some family planning advice,
explain the inheritance of red-green colorblindness
in their male children.
A nurse at a hospital removed the wrist tags of three babies in the maternity
ward. She needs to figure out which baby belongs to which parents, so she
checks their blood types. Using the chart below, match the baby to its correct
parents. Show the crosses to prove your choices
Parents
Blood Types
Baby
Blood type
Mr. Hartzel O
Mrs.
Hartzel
A
Jennifer
O
Mr. Simon
AB
Rebecca
A
Holly
B
Mrs. Simon AB
Mr. Peach
O
Mrs. Peach O