Page 51 - Genetics_From_Genes_to_Genomes_6th_FULL_Part1

Problems 43

called bHLH required by cells to make three differ- d. What is the probability that individual III-1 is
ent enzymes (DFR, ANS, and 3GT) that function in affected by the disease?
the pathway shown in the accompanying figure,
leading to synthesis of the purple pigment I
anthocyanin. 1 2 3 4
a. What is the most likely explanation for the difference II 1 2 3 4
between the dominant allele (P) and the recessive
allele (p) of the gene responsible for these flower III ?
colors?
b. Given the biochemical pathway shown, could a 37. A young couple went to see a genetic counselor be-
different gene have been the one governing Mendel’s cause each had a sibling with cystic fibrosis. (Cystic
flower colors? fibrosis is a recessive disease, and neither member of
the couple nor any of their four parents is affected.)
a. What is the probability that the female of this
Section 2.3 couple is a carrier?
35. For each of the following human pedigrees, in- b. What are the chances that their child will have
dicate whether the inheritance pattern is recessive cystic fibrosis?
or dominant. What feature(s) of the pedigree did
you use to determine the mode of inheritance? Give c. What is the probability that their child will be a
the genotypes of affected individuals and of indi- carrier of the cystic fibrosis disease allele?
viduals who carry the disease allele but are not 38. Huntington disease is a rare fatal, degenerative neu-
affected. rological disease in which individuals start to show
symptoms in their 40s. It is caused by a dominant al-
(a) I lele. Joe, a man in his 20s, just learned that his father
has Huntington disease.
II a. What is the probability that Joe will also develop
the disease?
III
b. Joe and his new wife have been eager to start a
IV family. What is the probability that their first child
will eventually develop the disease?
V
39. Is the disease shown in the following pedigree caused
by a dominant or a recessive allele? Why? Based on
(b) I this limited pedigree, do you think the disease allele
is rare or common in the population? Why?
II
I
III 1 2
II
1 2 3 4
(c) I III
1 2
II
40. Figure 2.22 shows the inheritance of Huntington
disease in a family from a small village near Lake
III
Maracaibo in Venezuela. The village was founded by
a small number of immigrants, and generations of
36. Consider the pedigree that follows for cutis laxa, a their descendants have remained concentrated in this
connective tissue disorder in which the skin hangs in isolated location. The allele for Huntington disease
loose folds. has remained unusually prevalent there.
a. Assuming that the trait is rare, what is the apparent a. Why could you not conclude definitively that the
mode of inheritance? disease is the result of a dominant or a recessive
b. What is the probability that individual II-2 is a allele solely by looking at this pedigree?
carrier? b. Is there any information you could glean from the
c. What is the probability that individual II-3 is a family’s history that might imply the disease is due
carrier? to a dominant rather than a recessive allele?