Page 90 - Genetics_From_Genes_to_Genomes_6th_FULL_Part1

82 Chapter 3 Extensions to Mendel’s Laws

a. Based on the pedigree, describe the dominance re- grandson back to the black mare gave a black foal,
lation between the wild-type and mutant alleles of and crossing a liver granddaughter back to the chest-
the gene for NADH diaphorase. nut stallion gave a chestnut foal. Explain how coat
b. The pedigree indicates certain people who were color is being inherited in these horses.
known to have only blue lips and fingertips. 22. Filled-in symbols in the pedigree that follows desig-
However, the historical record is incomplete. nate individuals who are deaf.
Which other people in the diagram must have had a. Study the pedigree and explain how deafness is
this phenotype? Explain any ambiguities that exist. being inherited.
(In case you’ve already read Section 3.3, assume b. What is the genotype of the individuals in genera-
that the blue lip and fingertip phenotype is fully tion V? Why are they not deaf?
penetrant.)
c. Two of the matings in the pedigree are shown as I
possibly consanguineous, as indicated by a dotted 1 2 3 4
horizontal line above a solid horizontal line. The II
reason for the uncertainty is that the historical re- 1 2 3 4 5 6 7 8
cord does not say whether or not Mary [Mary (?)], III
the wife of the Martin Fugate at the top left of the 1 2 3 4 5 6 7
diagram, was a Ritchie or a Smith or was instead un- IV
related to either family. Explain why a geneticist 1 2 3 4 5 6 7
would think that Mary is likely a Ritchie or a Smith. V
1 2 3 4 5 6 7 8 9 10 111213
d. All of the Blue People (people with methemo-
globemia) in the pedigree are Fugates, yet the blue 23. You perform a cross between two true-breeding
mutation did not originate in the Fugate family. strains of zucchini. One has green fruit and the other
Which person or people introduced the mutant has yellow fruit. The F 1 plants are all green, but
NADH diaphorase allele(s) into the Fugate family? when these are crossed, the F 2 plants consist of
9 green : 7 yellow.
Section 3.2 a. Explain this result. What were the genotypes of the
20. A rooster with a particular comb morphology called two parental strains?
walnut was crossed to a hen with a type of comb mor- b. Indicate the phenotypes, with frequencies, of the
phology known as single. The F 1 progeny all had wal- progeny of a testcross of the F 1 plants.
nut combs. When F 1 males and females were crossed c. Describe the epistasis interactions observed.
to each other, 93 walnut and 11 single combs were d. Suppose that the dominant alleles specify func-
seen among the F 2 progeny, but there were also tional enzymes, and the recessive alleles are non-
29 birds with a new kind of comb called rose and functional. Propose a biochemical pathway that
32 birds with another new comb type called pea. could explain the gene interactions.
a. Explain how comb morphology is inherited. e. Is it possible to cross two different pure-breeding
b. What progeny would result from crossing a homo- yellow zucchini strains and obtain all green prog-
zygous rose-combed hen with a homozygous eny? What would be the genotypes of the parents
pea-combed rooster? What phenotypes and ratios and progeny?
would be seen in the F 2 progeny? f. Assuming that wild-type zucchini are green, how
c. A particular walnut rooster was crossed to a pea would you describe the phenomenon that occurred
hen, and the progeny consisted of 12 walnut, in the F 1 of part (e)?
11 pea, 3 rose, and 4 single chickens. What are the 24. Two true-breeding white strains of the plant
likely genotypes of the parents? Illegitimati noncarborundum were mated, and the
d. A different walnut rooster was crossed to a rose F 1 progeny were all white. When the F 1 plants were
hen, and all the progeny were walnut. What are the allowed to self-fertilize, 126 white-flowered and
possible genotypes of the parents? 33 purple-flowered F 2 plants grew.
21. A black mare was crossed to a chestnut stallion and a. How would you describe inheritance of flower
produced a bay son and a bay daughter. The two off- color? Describe how specific alleles influence each
spring were mated to each other several times, and other and therefore affect phenotype.
they produced offspring of four different coat colors: b. A white F 2 plant is allowed to self-fertilize. Of
black, bay, chestnut, and liver. Crossing a liver the progeny, 3/4 are white-flowered, and 1/4 are