Question

Examine a two-gene cross that follows simple Mendelian inheritance of freckles and eyebrow shape between a woman with genotype Mmpp and a man with genotype mmpp. How many phenotypes are possible in their offspring and in what ratio?
a. 4 phenotypes: 9:3:3:1
b. 2 phenotypes; 1:1
c. 3 phenotypes; 8:4:4
d. 3 phenotypes; 1:2:1

Answer 1

Answer:

b

Explanation:

First, let us look at the result of crossing the two genotypes Mmpp and mmpp.

Mmpp will give the gametes Mp, Mp, mp, and mp

mmpp will give the gametes mp, mp, mp, and mp

The two sets of gametes can thus be lined up on both axis of the Punnet's square as shown in the attached image.

Genotypes of the offspring: 8 Mmpp and 8 mmpp

Since the two genes follow simple Mendelian inheritance pattern, the 2 genotypes automatically equates to 2 phenotypes in the ratio 1:1.

Hence, the correct option is b.