In Drosophila, the X-linked recessive mutation vermilion (v) causes bright red eyes, in contrast to the brick-red eyes of wild type. A separate autosomal recessive mutation, suppressor of vermilion (su-v), causes flies homozygous or hemizygous for v to have wild-type eyes. In the absence of vermilion alleles, su-v has no effect on eye color. Determine the F₁ and F₂ phenotypic ratios from a cross between a female with wild-type alleles at the vermilion locus, but who is homozygous for su-v, with a vermilion male who has wild-type alleles at the su-v locus.

Key Concepts

X-linked Inheritance

X-linked inheritance refers to the pattern of genetic transmission of traits located on the X chromosome. In Drosophila, males have one X chromosome and one Y chromosome, while females have two X chromosomes. This means that X-linked recessive traits, like the vermilion mutation, are more likely to be expressed in males, as they only need one copy of the recessive allele to show the trait.

Autosomal Recessive Inheritance

Autosomal recessive inheritance involves genes located on non-sex chromosomes (autosomes) where two copies of a recessive allele are required for the phenotype to be expressed. In this case, the suppressor of vermilion (su-v) is an autosomal recessive mutation that can mask the effects of the vermilion mutation when present in a homozygous or hemizygous state, demonstrating the interaction between different genetic loci.

Phenotypic Ratios in Genetic Crosses

Phenotypic ratios describe the relative frequencies of different observable traits in the offspring resulting from a genetic cross. In this scenario, understanding how to set up a Punnett square for the cross between the wild-type female (homozygous for su-v) and the vermilion male will help determine the expected ratios of eye color phenotypes in the F₁ and F₂ generations, illustrating the principles of inheritance and gene interaction.