Page 52 - Genetics_From_Genes_to_Genomes_6th_FULL_Part1

44 Chapter 2 Mendel’s Principles of Heredity

41. Consider the cystic fibrosis pedigree in Figure 2.24a. 44. Midphalangeal hair (hair on top of the middle
a. Assuming that one of the individuals in generation segment of the fingers) is a common phenotype
I was a carrier, and that no one from outside the caused by a dominant allele M. Homozygotes for
family was a carrier, what was the probability that the recessive allele (mm) lack hair on the middle
any single child of the consanguineous couple in segment of their fingers. Among 1000 families in
generation V would have cystic fibrosis? (Assume which both parents had midphalangeal hair, 1853
that none of their children is born yet, so you don’t children showed the trait while 209 children did not.
know that VI-4 has the disease.) Explain this result.
b. Assuming that one of the individuals in generation 45. A man with Huntington disease (he is heterozygous
+
I was a carrier and that 1/1000 people in the popu- HD HD ) and a normal woman have two children.
lation is a carrier, and knowing that VI-4 has a. What is the probability that only the second child
the disease, how likely was it that VII-1 would has the disease?
be affected? b. What is the probability that only one of the children
42. The common grandfather of two first cousins has he- has the disease?
reditary hemochromatosis, a recessive condition caus- c. What is the probability that none of the children
ing an abnormal buildup of iron in the body. Neither of has the disease?
the cousins has the disease nor do any of their relatives. d. Answer (a) through (c) assuming that the couple
a. If the first cousins had a child, what is the chance had 10 children.
that the child would have hemochromatosis? e. What is the probability that 4 of the 10 children in
Assume that the unrelated, unaffected parents of the family in (d) have the disease?
the cousins are not carriers.
b. How would your calculation change if you knew 46. Explain why disease alleles for cystic fibrosis (CF)
+
are recessive to the normal alleles (CF ), yet the
that 1 out of every 10 unaffected people in the pop- disease alleles responsible for Huntington disease
ulation (including the unrelated parents of these (HD) are dominant to the normal alleles (HD ).
+
cousins) was a carrier for hemochromatosis?
43. People with nail-patella syndrome have poorly devel- 47. The following pedigree shows the inheritance of red
hair in a family in Scotland. Red hair is caused by
oped or absent kneecaps and nails. Individuals with homozygosity for a recessive allele of a gene called
alkaptonuria have arthritis as well as urine that dark- MC1R. Although worldwide red hair is the rarest
ens when exposed to air. Both nail-patella syndrome of human hair colors, red hair is not uncommon in
and alkaptonuria are rare phenotypes. In the following Scotland. In fact, 40% of Scots without red hair are
pedigree, vertical red lines indicate individuals with nonetheless carriers of the red hair allele.
nail-patella syndrome, while horizontal green lines
denote individuals with alkaptonuria.
I
a. What are the most likely modes of inheritance of
nail-patella syndrome and alkaptonuria? What gen- II
otypes can you ascribe to each of the individuals in
the pedigree for both of these phenotypes?
III
b. In a mating between IV-2 and IV-5, what is the 1 2 9 10
chance that the child produced would have both IV ? ?
nail-patella syndrome and alkaptonuria? Nail- 1 2
patella syndrome alone? Alkaptonuria alone?
Neither defect? a. Why does red hair show a horizontal inheritance
pattern in this particular pedigree even though the
I
1 2 trait is caused by a recessive allele?
b. Assuming that individual III-2 has a child with the
II
1 2 3 4 5 6 Scottish woman shown (III-1) who is not a close
relative, what is the probability that this child
III
1 2 3 4 5 6 (IV-1) will have red hair?
c. What is the probability that the child of first cous-
IV
1 2 3 4 5 6 7 ins III-9 and III-10 (IV-2), will have red hair?