For the three pedigrees below determine the most likely mode

For the three pedigrees below, determine the most likely mode of inheritance of the trait exhibited by the shaded individuals. For Pedigrees the trait a rare and you can assume that who join the family through marriage are not Begin by eliminating those modes which would not give that pattern of inheritance. Consider the following possibilities: dominant, recessive, but x-linked determinant, x-linked recessive. Rare Disorder

Solution

The mode of inheritance in pedigree (A) is autosomal recessive,

Autosomal disorder because father to son the disorder is being transmitted which excludes the X-linked inheritance and Y-linked inheritance is also excluded as all males in every generation is not affected. There is a skip in generation II where both the parents are unaffected still the disorder is passed on.

The mode of inheritance in pedigree (B) is X-linked recessive,

Because in the pedigree mostly males are affected, the females are carrier, and when a female carrier cross with a healthy male the offspring will be affected. The daughters will always be a carrier. X-linked disorders generally affects males. Recessive as in first generation, both the parents are unaffected and second and third generation showed affected males.

The mode of inheritance in pedigree (C) is X-linked dominant,

The main observation was the transfer of disease/disorder from father(affected male) to every daughter of next generation and as the disease is X-linked no transmission of disorder from father to son. The disorder is present in every generation that is why dominant (no skip in generations).