Question

Complete Dominance – Dihybrid Crosses Methemoglobinemia is a recessive disorder characterized by a bluish tint to the skin. Individuals who are homozygous for this condition have an abnormally high level of methemoglobin versus normal hemoglobin. Not only does this tint the blood and therefore the skin, but methemoglobin does not deliver oxygen to the tissues as well as hemoglobin does, so tiredness and shortness of breath are common. M = normal, m = blue (methemoglobinemia). A family in Kentucky became known as the “blue Fugates” because of the frequent occurrence of the disorder. This was the result of marriage to close relatives. John Fugate is shown in the picture. Freckles (F) are dominant over no freckles (f), although the number of freckles differs among individuals (and with exposure to sun).

9. Zach is homozygous dominant for non-blue skin. He is heterozygous for freckles. His wife Mary is a carrier (heterozygous) for methemoglobinemia, and does not have freckles. What are the expected genotypic and phenotypic ratios for their children?

Answer 1

Genotype ratio :-

MMFf : MMff : MmFf : MmFf = 1:1:1:1.

Phenotype ratio :-

Normal skin, freckles ( MMFf and MmFf) : Normal skin, no freckles ( MMff and MmFf) = 1:1