Question

The given pedigree chart indicate

• A. X-linked dominant
• B. Autosomal dominant
• C. Autosomal recessive
• D. X-linked recessive
• E. Insufficient information
  

Answer 1

Answer: (D)

• In given pedigree, unaffected parents have affected offspring which means that either one or both parents are a carrier.
• It also shows recessive nature of the trait; if the trait was dominant it would have been expressed by heterozygous individuals as well. But heterozygous parents are serving as carrier only.
• In offspring, both sons and daughters are not equally; sons are affected. This means disease is not autosomal; if it was autosomal, both sons and daughters of carrier parents would be equally affected.
• The affected son of first offspring generation and normal female have all normal children.
• This means the trait is X linked recessive trait and affected father has passed the affected X chromosome to daughter.
• The daughter is carrier only because mother is normal. Likewise, normal females of first offspring generation and normal males have affected son showing that mother normal female is serving as a carrier. Trait is X-linked recessive.

Therefore, the correct answer is option D.