5.01 In an experiment designed to study the inheritance of flower color in four-o'clocks, two plants with pink flowers were crossed. In the progeny from this cross, there were 42 plants with red flowers, 86 with pink flowers, and 39 with white flowers. Using a chi-square test, determine whether those numbers are consistent with the single-gene, incomplete dominance inheritance pattern.

5.02 Trying to understand the inheritance of the dominant yellow gene in mice, researchers mated two yellow heterozygous mice. A typical result was 56 yellow progeny to 31 wild-type.

(a) Use a chi-square test to determine if the outcome of this cross is consistent with the usual 3:1 ratio predicted by Mendelian inheritance for a dominant gene.

(b) You will find that the chi-square test done in part (a) indicates the data are not consistent. Now try the hypothesis that the dominant allele is lethal in the homozygous condition. Repeat the chi-square test.

5.03 Which blood group type of the ABO system is known as the universal donor? Which type is the universal recipient? Explain your answers. Note: this is something we don't usually talk about in lecture, so you may have to look this up. It is not directly related to the inheritance pattern, but is worth knowing about because it is related to the properties of the red blood cells.

5.04 A woman with blood type A marries a man with blood type O.

(a) Given only this information, determine all the blood types that are possible for their children?

(b) Which blood types are not possible in the children?

(c) Would the answers to (a) or (b) change if it was known that both of the woman's parents had blood type AB? Explain.

5.05 A woman with type O blood, whose father has type A and whose mother has type B has a child with type O. There is a dispute over the identity of the child's father. Two men are possible fathers. One is type AB and the other is type A.

(a) What is the mother's genotype?

(b) Which man could be the father?

(c) If this man is the father, what is his genotype?

(d) What are the genotypes of the woman's parents?

5.06 In the peppered moth, Biston betularia, there is a gene that determine body color. Three alleles are possible for this gene. The allele for pale color (m) is recessive. A second allele (M’), which is dominant to m, produces a mottled color called insularia. The third allele (M), which is dominant to both of the other two, produces a melanic moth (very dark colored). A pale colored female moth is mated to a melanic male. If half the progeny are melanic and half are insularia, what were the genotypes of the two parents?

5.07 In a particular plant, there is a gene with five possible alleles, B₁, B₂, B₃, B₄, and B₅.

(a) Given that two plants with genotypes B₂B₄ and B₁B₅ are mated, what types of progeny, and in what proportions, would you expect?

(b) For the same gene, if a progeny from a single mating has equal numbers of B₁B₂ and B₂B₄ individuals (and no other genotypes), what are the parents' genotypes?

5.08 What is the difference between dominance and epistasis? Why didn't any pairs of genes used by Mendel show epistasis?

5.09 In chickens, comb shape is determined by two interacting genes (R/r and P/p). A walnut comb is produced when at least one dominant R allele and at least one dominant P allele are present (R- P-). A rose comb is produced when at least one dominantR allele is present and the second gene is homozygous recessive (R- pp). A pea comb is produced when the first gene is homozygous recessive and at least one dominant R allele is present (rr P-). When both genes are homozygous recessive, a single comb is produced. Predict the phenotype ratios for each of the following matings:

(a) RR PP X rr pp

(b) Rr pp X Rr pp

(c) Rr Pp X rr pp

(d) Rr pp X rr Pp

(e) Rr Pp X Rr Pp

(f) rr pp X rr Pp

5.10 As discussed in class, one form of fur color in mice is controlled by the interaction of two gene resulting in three phenotypes: agouti, black, and albino. Two agouti mice are crossed repeatedly, and the following offspring are produced: 46 agouti, 16 black, and 23 albino.

(a) Based on this cross, which common multiple gene inheritance pattern is operating here?

(b) Given your answer to part a, what were the genotypes of the parents?

(c) Show a forked-line diagram for this cross that makes it clear how each genotype category corresponds to each phenotype.

(d) For each of the following crosses, give the possible genotypes of the parents. Agouti x Agouti produces 37 agouti and 12 black Black x Albino produces 27 agouti and 24 albino Black x Black produces 28 black and 10 albino

5.11 The agouti fur color in mice actually results from alternating dark and light bands on each hair. Given this information and what you know about the gene interaction from the previous problem, propose a mechanism that could explain how each of the two genes is actually affecting the overall fur color (agouti, black, or albino).

5.12 In summer squash, there are two pairs of alleles that determine fruit color. The two genes sort independently. Two white-fruited plants are crossed. Both parents are known to be heterozygous for both genes. The cross produces the following offspring: 20 green-fruited plants, 58 yellow-fruited plants, and 218 white-fruited plants.

(a) Based on the observed ratio, which common type of epistasis is operating here? That is, which kind of modified dihybrid ratio most closely fits these data?

(b) List the four genotype classes in the offspring and give the corresponding phenotype of each.

(c) If a doubly heterozygous white plant is crossed with a green plant, what phenotype ratio would you expect in the progeny?

5.13 Two types of epistasis discussed were duplicate and complementary gene action. How would you distinguish between these types of epistasis in determining purple and white flower color if you could set up any crosses necessary?

5.14 The pedigree shown depicts the inheritance of a certain rare human disease. Solid symbols indicate diseased individuals; open symbols indicate normal individuals.

(a) How can you explain the observed pattern of inheritance? You can assume that each gene involved has a penetrance value of 1.0. That is, every individual with the appropriate genotype will exhibit the disease.

(b) Based on your explanation in part a, what are the genotypes of II-3 and II-4?

(c) If II-3 and II-4 have another child, what is the probability that he or she will have the disease?

(d) Assuming that this disease is very rare, what are the most likely genotypes of I-1, I-2, I-3, and I-4?

5.15 In wheat kernel color is determined by a pair of genes in a quantitative way. Each of the two genes can have two alleles (A₁, A₂, B₁, B₂). Kernel color ranges from red, when four type 1 alleles (either A₁ or B₁) are present, to white, when four type 2 alleles (either A₂ or B₂) are present. Three intermediate colors (dark pink, medium pink, and light pink) can occur depending on the relative numbers type 1 and type 2 alleles (this example was discussed in lecture). Using the forked-line approach, calculate the expected proportions of the five phenotypes that would be produced by a cross between two wheat plants with medium pink kernels that are heterozygous for both genes: A₁A₂ B₁B₂ x A₁A₂ B₁B₂ .