In the following pedigree chart, the mutant trait is shaded black. The gene responsible for the trait is

Options

A. dominant and sex linked
B. dominant and autosomal
C. recessive and sex linked
D. recessive and autosomal

Answer

D

Explanation

The given trait cannot be sex-linked as sex-linked traits follow criss-cross inheritance and in the given pedigree, no criss-cross inheritance us being followed.
The trait exhibited in pedigree chart is autosomal recessive. An autosomal recessive trait appears in case of marriage between two heterozygous individuals `(Aa xx Aa = 3 Aa + 1 aa`), a recessive individual with hybrid `(Aa xx aa = 2 Aa + 2aa)` and two recessives `(aa xx aa = all aa)`. It expresses its effect only in pure or homozygous state
If the trait had been controlled by dominant gene, then one of the parent must have possessed the dominant gene and hence the disease.