Question

11 the pedigree below represents an inherited disorder. pedigree key carrier female affected female affected male nonaffected male nonaffected female what mode of inheritance is shown? a x - linked dominant b x - linked recessive c autosomal dominant d autosomal recessive

Explanation:

• X - linked dominant: If it were X - linked dominant, affected males would pass the trait to all their daughters (since daughters get the X from the father). But here, the affected male in the second generation has a non - affected daughter. So it's not X - linked dominant.
• Autosomal dominant: If it were autosomal dominant, at least one of the parents of an affected individual would be affected (assuming no new mutations). But the affected male in the second generation has a non - affected father and a carrier mother. So it's not autosomal dominant.
• Autosomal recessive: If it were autosomal recessive, two non - affected parents could have an affected child (if both are carriers). But the pattern in the pedigree doesn't match typical autosomal recessive (where males and females are affected with similar frequencies in some cases, but here the key is the X - linked pattern clues).
• X - linked recessive:
• Males have one X chromosome. An affected male (with the recessive allele on his X) can pass the X to his daughters. Daughters need two recessive alleles (one from each parent) to be affected, but carriers (with one recessive allele) are shown. Sons get the Y from the father. In the pedigree, affected males have carrier daughters (who get the X with the recessive allele from the father), and carrier females can have affected sons (who get the X with the recessive allele from the mother).

Answer:

B. X - linked recessive