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).

10. Manuel Fugate marries his cousin Polly Ritchie. Both are carriers for methemoglobinemia. Both are also heterozygous for freckles. What is the expected phenotypic ratio for their children?

Answer 1

Answer-

Since methhemoglobinemia is a recessive disorder genotypes are as follows-

MM - normal

Mm - carrier but appears normal

mm - affected with methhemoglobinemia.

Mm individuals are counted as normal phenotype along with MM in phenotypic ratio as they do not suffer from the disease only carry one revesaive allele which is carried onto next generation.

Freckles is completely dominant over not having freckles so F is completely dominant over f so even in heterozygous conditions , Ff , freckles will be expressesd as phenotype .

So in the image genotypes underlined with pink are normal Hb, freckled individuals includes genotypes MM FF , MmFf ,MmFF, MMFf .

Circled with pink are normal Hb, non freckled individuals.

Double underlined with blue are Methhemoglobinemia, freckled individuals .

Circled with pen is methhemoglobinemia affected and non - freckled individuals.

If this helps please give it a positive rating thank you!