In fruit flies, red eyes (pr+_)are dominant to purple eyes (prpr)and normal wings (vg+_)are dominant to vestigial wings (vgvg). The genes are located on the same chromosome. A purebreeding red-eyed fly with vestigial wings was crossed with a pure-breeding purple-eyed fly with normal wings. All of the F₁ progeny had a WT phenotype. Which of the following represents the arrangement of alleles on the F₁'s chromosome?

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Quizplus · Accepted Answer

The parental flies are pure-breeding, so the red-eyed fly with vestigial wings must be homozygous dominant for both traits (pr+vg/ pr+vg) and the purple-eyed fly with normal wings must be homozygous recessive for both traits (prprvgvg/prprvgvg). The F1 generation will all be heterozygous for both traits (pr+vg/prvg), since they each received one dominant and one recessive allele from each parent. When the F1 generation is crossed, the offspring will have a WT phenotype, indicating that they received at least one dominant allele for both traits. The only genotype that corresponds to this phenotype is pr+vg/prvg+. Therefore, the arrangement of alleles on the F₁'s chromosome is pr+vg/prvg+.

In Fruit Flies, Red Eyes (Pr+_)are Dominant to Purple Eyes