Five recessive mutations on the right arm of the X chromosome of Drosophila mela
ID: 86011 • Letter: F
Question
Five recessive mutations on the right arm of the X chromosome of Drosophila melanogaster cause stringy bristle (sg), lazy eyes (ly), tin body (tn), zillion eye (ze), and miniature wing (m) phenotypes. Two wildtype male flies were exposed to X-rays and then mated separately with (non-irradiated) females showing all five recessive traits (Mating 1 and Mating 2). a) Mating 1 produced normal females and sg ly tn ze m males in equal proportions. One of these phenotypically normal females, when mated to a male sibling, produced F2 progeny that consisted solely of normal and fully mutant phenotypes. Why was this result unexpected, and how do you explain it? b. Mating 2 produced sg ly tn ze m males and ly tn females in equal proportions. Explain the result.Explanation / Answer
Answer
a). In mating 1, all five genes are not mutated in the male drosophila, and all five gene homozygous recessive in female. Hence, all female progeny are wild (carrier or heterozygous) and all males are recessive for all traits.
During siblings mating, 50% females are heterozygous wild phenotypes and remaining 50% females are recessive phenotypes and 50% males are wild phenotypes and remaining 50% males are recessive phenotypes.
b). In mating 2, only two genes that are lazy eyes and tin body are mutated in males and female is recessive for all traits. Hence females are recessive for lazy eyes and tin body and remaining three genes are heterozygous and they show wild phenotypes.
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