Solved by a verified expert:PCB 3063– Sec 799
Summer C 2016
Question 5: (5 points)
Shown below is
the pedigree of a rare neurodegenerative disease in humans.
a. Based on the pedigree,
characterize each of the following modes of inheritance as likely, unlikely, or
impossible: autosomal dominant, autosomal recessive, Y linked, X-linked dominant,
and X-linked recessive. Justify your reasoning.
Further scrutiny of members of
this family reveals the following: 1) The disease’s degree of expression varies
among individuals, with some mildly affected, others moderately affected and
still others severely affected; and 2) Individual III-14 was previously
married. Her ex-husband is phenotypically normal, with no history of the
disease in his family going back ten
generations. He has custody of the couple’s two children, a girl and a boy,
both of whom are affected with the disease. The partial pedigree is shown below
(the “slash” represents separation or divorce)
b. Do these findings eliminate
any of the remaining “likely or unlikely” modes of inheritance listed in part (a)? Are any of these modes of
inheritance still possible? If so, which one(s) and why?
c. Is mitochondrial
inheritance a likely, unlikely or an impossible mode of inheritance for this
disease? Does it provide an explanation for the disease’s variable
expressivity?
d. How can mitochondrial
inheritance explain individual III-14?
Question 6: (2 points)
In a human population, the frequencies of alleles A and a are 0.8 and 0.2, respectively. Assume gene A is autosomal and the population is under Hardy-Weinberg
equilibrium. If five people are randomly
selected, what is the probability that exactly
3 AA and 2 Aa individuals will be picked?
Question 7: (3 points)
As we
discussed in “lecture” earlier in the semester,Rh is the most complex
of the blood group types, involving at least 45 different antigens. The most
clinically important antigen, D or RhO, is encoded by the gene RhDwhich is found on chromosome 1.
Individuals that are Rh-positive have either one or two RhD genes, whereas the Rh-negative phenotype is caused by the
absence of the RhD gene. (The
antithetical allele d does not exist,
however the letter “d” is used to indicate the D-negative phenotype).
For the purpose of this homework, we will simplify things. Assume that the Rh
blood group has only two alleles: the Rh-positive allele (D) and the Rh-negative allele (d).
Erythroblastosis fetalis (EF)is a condition that causes the mother’s red blood cells to attack
those of the baby as if they were any foreign invaders. It is referred to as
hemolytic anemia of the newborn. It is caused by anti-Rh antibodies from the
mother which pass through the placenta and attack fetal blood cells that happen
to be Rh-positive. Babies that are at risk for this condition are those with
Rh-positive blood, whose mothers are Rh-negative (dd).
Side note:Here’s a headline from last year that addresses this condition. It’s
well worth a read!
http://www.cnn.com/2015/06/09/health/james-harrison-golden-arm-blood-rhesus/index.html
Consider
a population under Hardy-Weinberg equilibrium, where the frequency of the
Rh-negative allele, d, is 0.3. What
is the frequency of crosses that could potentially produce children with
erythroblastosis fetalis?
Question 8: (3 points)
ABO blood type is studied in a Lebanese population, and these
allele frequencies are determined.
f(IA)
0.30
f(IB)
0.15
f(IO)
0.55
What are the frequencies of the various genotypes and
various phenotypes in this population? Assume Hardy-Weinberg equilibrium.
Question 9: (3 points)
In humans, the presence of chin
and cheek dimples is dominant to the absence of dimples, and the ability to
taste the bitter compound PTC (phenylthiocarbamide) is dominant to the
inability to taste this compound. Both traits are under the control of
autosomal genes that are unlinked.
A population from Ghana is examined, and the following
allele frequencies are calculated.
Dimples
Frequency
Tasting
Frequency
D
0.62
T
0.76
d
0.38
t
0.24
a. Determine
the frequency of genotypes for each gene.
b. What
are the expected frequencies of the four possible phenotype combinations:
dimpled tasters, undimpled tasters,
dimpled nontasters, and undimplednontasters?
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