Question

If the characteristic followed in the pedigree is X-linked recessive allele, what is III-1's genotype?

a. Hemizygous for a dominant allele
b. Hemizygous for a recessive allele
c. Definitely heterozygous
d. Definitely homozygous dominant
e. Either heterozygous or homozygous dominant

Answer 1

In X-linked recessive inheritance, males can express the trait if they inherit the recessive allele. Therefore, III-1's genotype in the given pedigree is definitely homozygous for the recessive allele.

Step-by-step explanation:

In X-linked recessive inheritance, the recessive allele is located on the X chromosome. Males have one X chromosome and one Y chromosome, so if they inherit the recessive allele, they will express the trait. Females have two X chromosomes, so they need to inherit the recessive allele from both parents to express the trait.

In the given pedigree, III-1 is a male. Since the trait being followed is X-linked recessive, if III-1 expresses the trait, it means he has inherited the recessive allele from his mother. Therefore, III-1's genotype is homozygous for the recessive allele. So the correct answer is c. Definitely homozygous.