Question

Which of the following is generally true of an autosomal recessive pedigree?
A. On average, 50% of the children will have the autosomal recessive disease if one parent has the disease.
B. Males are affected more than females.
C. On average, 25% of the children are affected by the autosomal recessive disease if both parents are carriers.
D. There is a decreased risk of disease with consanguinity.

Answer 1

Answer:

C. On average, 25% of the children are affected by the autosomal recessive disease if both parents are carriers.

Explanation:

A recessive trait is always expressed in homozygous genotype only. To have progeny with recessive traits from two normal parents, both the parents should be heterozygous carriers. For example, two normal parents with genotype "Aa" have 25% of the chances to have a child with homozygous recessive genotype (Aa x Aa = 1/4 AA: 1/2 Aa: 1/4 aa).

An autosomal trait is equally expressed in both males and females. Inbreeding increases the homozygosity and thereby, increases the risk of expression of recessive traits which are otherwise masked in heterozygous genotype.