Question

This is an example of sex-influenced genes. Fill in the appropriate genotypes at positions 1, 2, 3 and 4.

• A. 1- BB, 2- Bb, 3- bb, 4- bb
• B. 1- Bb, 2- BB, 3- bb, 4- bb
• C. 1- BB, 2- Bb, 3- Bb , 4- bb
• D. 1- bb, 2- Bb, 3- BB, 4- Bb

Answer 1

Answer: (A)

According to the question, baldness is a sex influenced trait. The homozygous genotypes (BB) show the trait irrespective of their sex. The heterozygous male express the trait but females with same genotype are normal. The boy at position 1 gets "B" allele from mother and other "B" allele from father, hence, its genotype is "BB (bald)". The boy at position 2 gets "b" allele from mother and "B" allele from father, hence, its genotype is "Bb (bald)". The boy at position 3 gets "b" allele from mother and other "b" allele from father, hence, its genotype is "bb (non-bald)". The girl at position 4 gets "b" allele from mother and other "b" allele from father, hence, its genotype is "bb (non-bald)". Hence, the genotypes are 1- BB, 2- Bb, 3- bb, 4- bb.

Thus, the correct answer is option A.