Question

In the laboratory, a graduate student isolated a mutant male fly that has short bristles (normal flies have long bristles). You crossed some F1 males with short bristles with F1 females with short bristles, and obtained the following results: 30 males with short bristles, 16 males with long bristles, 31 females with short bristles, and 15 females with long bristles. Please indicate the genetic basis for the short bristle mutation.

1) Autosomal dominant
2) Autosomal recessive
3) Recessive lethality
4) X-linked dominant
5) X-linked recessive

Answer 1

The short bristle mutation in the studied Drosophila is autosomal recessive, as evidenced by the 3:1 phenotypic ratio of short to long bristles in both male and female offspring. (option 2)

Step-by-step explanation:

In a cross between F1 males and females with short bristles, the observed ratio of 30:16 short-bristled males to long-bristled males and 31:15 short-bristled females to long-bristled females suggests a 3:1 phenotypic ratio for both sexes. This is indicative of a classic Mendelian recessive trait.

The F1 generation results from the cross of two heterozygous individuals, each carrying one normal and one mutant allele. The presence of long-bristled individuals in the F1 generation indicates that the trait is not dominant. The 3:1 ratio is characteristic of a monohybrid cross involving a recessive trait.

Considering the equal distribution of the trait between males and females, and the absence of a sex-linked pattern, the short bristle mutation is likely autosomal. The consistent phenotypic ratios across genders support the conclusion that the mutation is autosomal recessive.

The short bristle mutation follows an autosomal recessive pattern, as evidenced by the 3:1 phenotypic ratio in both males and females in the F2 generation.