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Q.
In the following pedigree chart, the mutant trait is shaded black. The gene responsible for the trait is
Principles of Inheritance and Variation
Solution:
The given trait cannot be sex-linked as sex-linked traits follow criss-cross inheritance and in the given pedigree, no criss-cross inheritance is being followed. The trait exhibited in pedigree chart is autosomal recessive. An autosomal recessive trait appears in case of marriage between two heterozygous individuals $(Aa \times Aa = 3 \,Aa + 1aa)$, a recessive individual with hybrid $(Aa \times aa = 2Aa + 2aa) $ and two recessives $(aa \times aa =$ 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.
