Question

How many recessive alleles must a female possess to express an X-linked recessive trait like haemophilia?

Options

• Three or more recessive alleles across both chromosomes

• Two recessive alleles, one on each X chromosome

• A single recessive allele inherited from the father

• Only one recessive allele on one X chromosome

Answer 1

Females possess two X chromosomes. To express an X-linked recessive trait, they must be homozygous recessive, meaning both X chromosomes carry the recessive allele. A female with only one recessive allele is a carrier and does not express the trait phenotypically.