Biology 11th Edition by Gerald Audesirk,Teresa Audesirk,Bruce Byers

Exercise 18

In humans, hair color is controlled by two interacting genes. The same pigment, melanin, is present in both brown-haired and blond-haired people, but brown hair has much more of it. Brown hair ( B ) is dominant to blond ( b ). Whether any melanin can be synthesized depends on another gene. The dominant form of this second gene ( M ) allows melanin synthesis; the recessive form ( m ) prevents melanin synthesis. Homozygous recessives ( mm ) are albino. What will be the expected proportions of phenotypes in the children of the following parents?
a. BBMM × BbMm
b. BbMm × BbMm
c. BbMm × bbmm