Page 138 - Genetics_From_Genes_to_Genomes_6th_FULL_Part1

130 Chapter 4 The Chromosome Theory of Inheritance

What are the genotypes of the following individuals? 40. The X-linked gene responsible for DMD encodes a pro-
c. individual I-1 tein called dystrophin that is required for muscle func-
d. individual I-8 tion. Dystrophin protein is not secreted—it remains in
the cells that produce it. Given what you know about
e. individual I-9 Barr body formation, do you think that females hetero-
f. individual II-6 zygous for the recessive DMD disease allele could have
g. individual II-8 the disease in some parts of their bodies and not others?
h. individual III-4 41. Males have hemophilia when they are hemizygous for
a nonfunctional recessive mutant allele of the X-linked
gene for clotting factor VIII. Factor VIII is normally
I
1 2 3 4 5 6 7 8 9 secreted into the blood serum by cells in the bone
marrow (and other specialized cells) that produce it.
II
1 2 3 4 5 6 7 8 9 a. Do you think that females heterozygous for the
III hemophilia disease allele could have hemophilia
1 2 3 4 5 6 7 in some parts of their bodies and not others?
IV b. If such a female carrier of hemophilia suffered a
1
cut, would her blood coagulate (form clots) faster,
39. Duchenne muscular dystrophy (DMD) is caused by a slower, or in about the same time as that of an indi-
relatively rare X-linked recessive allele. It results in vidual homozygous for a normal allele of the factor
progressive muscular wasting and usually leads to VIII gene? Would the rate of clotting vary signifi-
death before age 20. In this problem, an affected cantly among heterozygous females?
person is one with the severe form of DMD caused by
hemizygosity or homozygosity for the disease allele. 42. In the Fast Forward Box Visualizing X Chromosome
a. What is the probability that the first son of a Inactivation in Transgenic Mice, suppose the investiga-
tors had looked at the expression of green and red fluo-
woman whose brother is affected will be affected? rescent protein in early mouse embryos, when the
b. What is the probability that the second son of a embryos have fewer than 500 cells. What patterns would
woman whose brother is affected will be affected, they likely have observed? (Assume that the transgenes
if her first son was affected? make gene product this early in development.)
c. What is the probability that a child of an unaffected 43. The following pedigree shows five generations of a family
man whose brother is affected will be affected? that exhibits congenital hypertrichosis, a rare condition in
d. An affected man mates with his unaffected first which affected individuals are born with unusually abun-
cousin; there is otherwise no history of DMD in dant amounts of hair on their faces and upper bodies. The
this family. If the mothers of this man and his mate two small black dots in the pedigree indicate miscarriages.
were sisters, what is the probability that the a. What can you conclude about the inheritance of
couple’s first child will be an affected boy? An hypertrichosis in this family, assuming complete
affected girl? An unaffected child? penetrance of the trait?
e. If the two related parents of the couple in part (d) b. On what basis can you exclude other modes of
were brother and sister (instead of sisters), what is inheritance?
the probability that the couple’s first child will be an c. With how many fathers did III-2 and III-9 have
affected boy? An affected girl? An unaffected child? children?

I

II

III 3 2

IV 2 2 2

V