Sex-linked Inheritance of Color-blindness Solutions

            In a pedigree, squares represent males while circles represent females. Shaded circles or squares indicate an affected individual.

a) Consider the cross between a color-blind female and a normal male. Construct a Punnett square for the cross. If color-blindness is recessive, what are the phenotypes of the female and male children of the cross? (all female will be carriers; all males will be color-blind)

b) If one of the daughters in the cross above married a color-blind man, what are the chances of them having a color-blind son? (chance of having a color-blind son is 1/2 x 1/2 although half of sons will be color-blind) A color-blind daughter? (chance of having a color-blind daughter is 1/2 x 1/2 although half of daughters will be color-blind)

c) What are the phenotypes of the original parents in the pedigree in Figure 1? (mother normal; father color-blind)

d) How can you be sure the genotype of the daughter of the original parents is heterozygous? (male child is color-blind, therefore, must have received color-blind allele from mother)

e) Can the genotype of the original female be determined? (No. She could be homozygous or heterozygous and still produce children with the given genotypes)

f) Could the sons have color-blind daughters. Explain. (No. The X chromosome they receive from their father would have the normal vision allele)

g) Would it be possible for the sons to have color-blind sons? Explain. (Only if the mother were a carrier or color-blind)

h) Fill in the genotype for each individual in the pedigree in Figure 2. (A - X^cX^c; B - X^Cy; C - X^Cy; D - X^CX^c; E - X^CX^c; F - X^cy; G - X^cy; H - X^CX^c; I - X^Cy; J - X^cy; K - X^cX^c)

i) Show the possible phenotypes and genotypes from the cross between individuals C and D. (X^CX^C, X^Cy, X^CX^c, X^cy; males with normal or color-blind vision, females with normal vision)