Question

The following two pedigree describe the autosomal genetic disorders P and Q in Family $1$ and Family $2$, respectively.
Choose the correct statement from the following options.

• A. Both P and Q are dominant traits.
• B. P is a dominant trait and Q is a recessive trait.
• C. Both P and Q are recessive traits.
• D. P is a recessive trait and Q is a dominant trait.

Answer 1

Answer: (B)

P is a dominant trait and Q is a recessive trait.

In the pedigree of family 1, the P disorder is an autosomal dominant trait. The female is having the defective gene whereas the male is having the normal gene in generation I. The defective gene is transferred from mother to the I-1, I-4, I-6 children and these children are affected. Whereas normal gene is transferred from mother to rest of the children. Since II-2 and II-3 both are unaffected, their all children are normal.

In the pedigree of family 2, the Q disorder is an autosomal recessive trait. In generation I, the female is having two copies of defective genes whereas as male is having only one copy of the defective gene. Hence, the male is a carrier of the disorder. The defective gene is transferred from mother to all her children in II generation. Whereas only II-6 daughter received defective gene from the father. All the other children are the carrier of the disorder. Normal gene is transferred from II-2 and II-3. Hence, all their children are normal.

Thus, the correct answer is option B.