Page 91 - Genetics_From_Genes_to_Genomes_6th_FULL_Part1

Problems 83

purple-flowered. What is the genotype of the white that the child is not his. Do you think that the wife is
F 2 plant? necessarily guilty of adultery? Explain.
c. A purple F 2 plant is allowed to self-fertilize. Of the 31. The following table shows the responses of blood
progeny, 3/4 are purple-flowered, and 1/4 are samples from the individuals in the pedigree to anti-A
white-flowered. What is the genotype of the purple and anti-B sera. A plus (+) in the anti-A row indicates
F 2 plant? that the red blood cells of that individual were
d. Two white F 2 plants are crossed with each other. clumped by anti-A serum and therefore the individual
Of the progeny, 1/2 are purple-flowered, and 1/2 made A antigens, and a minus (−) indicates no
are white-flowered. What are the genotypes of the clumping. The same notation is used to describe the
two white F 2 plants? test for the B antigens.
25. Suppose the intermediate called Colorless precursor 2 I-1 I-2 I-3 I-4 II-1 II-2 II-3 III-1 III-2
in the pathway shown in Fig. 3.16 was blue instead of anti-A + + – + – – + + –
colorless.
anti-B + – + + – – + – –
a. What would be the phenotypic ratio of the F 2 ?
(Blue color is distinct from purple.) I
1 2 3 4
b. Describe the type of genetic interaction that corre- II
sponds to this new phenotypic ratio. 1 2 3
26. Explain the difference between epistasis and domi- III 1 2
nance. How many loci are involved in each case?
27. The dominant allele H reduces the number of body a. Deduce the blood type of each individual from the
bristles in fruit flies, giving rise to a hairless pheno- data in the table.
type. In the homozygous condition, H is lethal. The b. Assign genotypes for the blood groups as accu-
dominant allele S has no effect on bristle number ex- rately as you can from these data, explaining the
cept in the presence of H, in which case a single S al- pattern of inheritance shown in the pedigree.
lele suppresses the hairless phenotype, thus restoring Assume that all genetic relationships are as pre-
the bristles. However, S is also lethal in homozygotes. sented in the pedigree (that is, there are no cases of
a. What ratio of flies with normal bristles to hairless false paternity).
individuals would we find in the live progeny of a 32. Three different pure-breeding strains of corn that pro-
cross between two normal flies both carrying the duce ears with white kernels were crossed to each
H allele in the suppressed condition? other. In each case, the F 1 plants were all red, while
b. When the hairless progeny of the previous cross are both red and white kernels were observed in the F 2
crossed with one of the parental normal flies from generation in a 9:7 ratio. These results are summa-
part (a) (meaning a fly that carries H in the sup- rized in the following table.
pressed condition), what phenotypic ratio would F 1 F 2
you expect to find among their live progeny? white-1 × white-2 red 9 red : 7 white
28. Secretors (genotypes SS and Ss) secrete their A and B white-1 × white-3 red 9 red : 7 white
blood group antigens into their saliva and other body white-2 × white-3 red 9 red : 7 white
fluids, while nonsecretors (ss) do not. What would be
the apparent phenotypic blood group proportions a. How many genes are involved in determining
A B
A A
among the offspring of an I I Ss woman and an I I kernel color in these three strains?
Ss man if typing was done using saliva? b. Define your symbols and show the genotypes for the
29. Normally, wild violets have yellow petals with dark pure-breeding strains white-1, white-2, and white-3.
brown markings and erect stems. Imagine you dis- c. Diagram the cross between white-1 and white-2,
cover a plant with white petals, no markings, and showing the genotypes and phenotypes of the F 1
prostrate stems. What experiment could you perform and F 2 progeny. Explain the observed 9:7 ratio.
to determine whether the non-wild-type phenotypes 33. In mice, the A allele of the agouti gene is a recessive
Y
are due to several different mutant genes or to the lethal allele, but it is dominant for yellow coat color.
pleiotropic effects of alleles at a single locus? Explain What phenotypes and ratios of offspring would you
how your experiment would settle the question. expect from the cross of a mouse heterozygous at the
30. A woman who is blood type B has a child whose agouti gene (genotype A A) and also at the albino
Y
blood type is A; her husband is blood type O. Despite gene (Cc) to an albino mouse (cc) heterozygous at the
Y
his wife’s claims of innocence, the irate father claims agouti gene (A A)?