2. Color blindness is also a recessive X-linked gene. Let's denote the
normal and mutant alleles as Xb+ and Xb respectively. A woman with
genotype Xb+/Xb marries a man of genotype Xb/Y. They have four sons and
two daughters.
a. On average, how many of the sons will be color blind?
b. On average, how many of the daughters will be color blind?
c. On average, how many of the daughters will be carriers for the Xb allele?
3. The Xg blood group is an X-linked trait. Having the Xg+ allele for the Xg-positive blood type is dominant to having the Xg allele that doesn't produce this blood type. If a man who is Xg+/Y marries a woman who is Xg/Xg, what percentage of their sons will have the Xg positive blood type? What percentage of their daughters will have it?
4. For the X-linked hemophilia gene, the frequency of the normal allele is
0.95 and the frequency of the mutant allele is 0.05. Keeping in mind the
difference in how X-linked genes affect the sexes, what is the probability
that a man will have hemophilia? And a woman?
(Note: this hemophilia allele frequency is way too high, I think!!)
5. A phenotypically normal woman of unknown genotype for the hemophilia gene,
marries a normal man of genotype Xh+/Y. Using the same allele
frequencies as before:
(a) What is the probability that their child has hemophilia?
(b) What is the probability that their child is a carrier for hemophilia?
(c) What is the probability that their child
is normal and not a carrier for hemophilia?
6. A man who is color-blind and has genotype Xb/Y, marries a woman of normal
phenotype and unknown genotype. The frequency of the normal
color-blindness allele (Xb+) is 0.8, and of the mutant color-blindness
allele is 0.2.
(Note: again the allele frequency is too high!!)
Remembering that this disease is X-linked:
(a) What is the probability that their child is color-blind?
(b) What is the probability that their child is a carrier?
(c) What is the probability that their child is phenotypically normal?
(that is, not color blind).