Question

Haemophilia is a sex-linked recessive disease. Study the pedigree analysis given showing the inheritance of the disease in a family and answer the questions that follow.
Give the evidence from the analysis, which suggests that the disease is sex-linked and caused by a recessive allele.

Answer 1

X-Linked Recessive

• More males than females are affected

• Affected sons are usually born to unaffected

mothers, thus the trait skips generations

• Approximately 1/2 of carrier mothers’ sons are affected

• It is never passed from father to son

• All daughters of affected fathers are carriers.

All these characters are being satisfied in this case. So the disease is a sex-linked recessive trait as evident from the pedigree chart analysis.