Question

a biologist studying the inheritance of a disease observed that the disease occurred in a family after three generations. the second and third generation showed no symptoms of the disease. she made a pedigree to analyze the inheritance pattern of the disease
after analyzing the data, what conclusion can the biologist make?
the disease occurs more often in males
the disease is rare in the general population.
the disease occurs in alternate generations
the disease is autosomal recessive

Explanation:

• The disease occurred in the first generation (affected female), skipped the second and third generations (no symptoms), and reappeared in the fourth generation (affected males). This pattern of skipping generations is characteristic of a recessive trait.
• Since both males and females can be carriers (unaffected in skipped generations) and the trait is not showing a sex - linked bias (if it were sex - linked, there would be a more pronounced male - only or female - only pattern in some cases), it is likely autosomal recessive.
• Just because it occurred in a family does not mean it is rare in the general population (no data on general population).
• Only two affected males are shown, and there is not enough data to conclude it occurs more often in males.
• The disease occurred in the first and fourth generations (not strictly alternate generations in a simple 1 - 2 - 3 - 4 sense, but the key is the skipping of generations which is a hallmark of recessive inheritance).

Answer:

The disease is autosomal recessive.