A trait appears in siblings but not in the parents for two generations; which mode of inheritance is most likely?

• A. Autosomal recessive
• B. Autosomal dominant
• C. X-linked dominant
• D. Mitochondrial inheritance

Answer: (A)

This pattern points to an autosomal recessive inheritance. When both parents are carriers but unaffected, their children can be affected even though neither parent shows the trait. This allows the trait to appear in siblings while skipping generations, and it affects males and females roughly equally because the gene is on an autosome. In autosomal dominant inheritance, you’d expect the trait to appear in every generation and be present in at least one parent. X-linked dominant would show distinct transmission through daughters and often one affected parent to multiple offspring, while mitochondrial inheritance would pass from mothers to all their children, not skipping generations in this way. So the most likely mode is autosomal recessive.