There are a lot of wing mutations for Drosophila. You areobserving a new mutatio
ID: 3438 • Letter: T
Question
There are a lot of wing mutations for Drosophila. You areobserving a new mutation that codes for crinkled wings.a. When a true-breeding crinkled-wing fly is crossed with atrue-breeding apterous (no wings) fly, all of the F1 progeny arewild type. The same results are seen for the reciprocalparental cross. What can you conclude about these mutationsand the gene(s) that code for them? Explain answer.
b. Two of the F1 flies were then crossed producing a large F2generation consisting only of wild type, crinkled, and apterousflies in a 9:3:4 ratio. What can you conclude from progenyfrom this cross? Explain answer.
Explanation / Answer
a) This type of inheritance looks like Epistasis, "the interactionbetween genotypes at two different gene loci, which sometimesresembles a dominance interaction at a single locus"(wikipedia). Basically there are two loci involved for theobserved phenotype. One loci may be responsible for the wingsshape, crinkled or normal/wildtype. We will call the crinkledallele 'c' and it is recessive to the wildtype allele'C'. Another loci may be responsible for the wing growth/presence, apterous (no wings) or with wings/wildtype. We willcall the apterous allele 'a' and it's recessive to the wildtype'A'. Neither of these traits are sexlinked. b) The genotype of the true breeding crinkled fly is ' ccAA'. The genotype of the true breeding apterous fly is ' CC aa' Their F1 progeny will all have the same phenotype (wildtype) andgenotype 'Cc Aa' The cross for the F2 is a follows: Cc Aa x Cc Aa CA Ca cA ca CA CCAA CCAa CcAA CcAa Ca CCAa CCaa CcAa Ccaa cA CcAA CcAa ccAA ccAa ca CcAa Ccaa ccAa ccaa CCAA: 1 -------Wildtype CCAa: 2 --------Wildtype CCaa: 1 ---------Apterous CcAA: 2---------Wildtype CcAa: 4 ---------Wildtype Ccaa: 2 ----------Apterous ccAA: 1----------Crinkled ccAa: 2 ----------Crinkled ccaa: 1 -----------Apterous So there are 9 genotypes and 3 phenotypes. CCAA, CCAa, CcAA, and CcAa all yield the wildtype. There are 9 ofthese genotypes in the punnet square ccAA and ccAa yiled crinkled. There are 3 of these genotypes in thepunnet square. CCaa, Ccaa, and ccaa yield apterous. The are 4 of these genotypesin the punnet square. So the ratio of 9:3:4 is confirmed. Also ccaa is homozygous for both crinkled and apterous wings butthe apterous alleles are "dominant" over the crinkled alleles asthey prevent wing presence, crinkled or otherwise.
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