In Drosophila melanogaster , a recessive autosomal allele, black ( b ), produces
ID: 8734 • Letter: I
Question
In Drosophila melanogaster, a recessive autosomal allele, black (b), produces a black body color when homozygous. An independently assorting autosomal allele, ebony (e), also produces a black body color when homozygous. Flies with the genotypes b+/- e/e, b/b e+/- and b/b e/e display an identical black body color phenotype, while flies of genotype b+/- e+/- have a grey body color. True-breeding b+/b+ e/e ebony flies are crossed to true-breeding b/b e+/e+ black flies, and the F1 progeny are crossed together. What phenotypes and proportions do you expect in the F2 generation?
A. All black F2 B. 9 black: 7 grey C. 9 grey: 7 black D. 15 black: 1 grey E. 15 grey: 1 blackExplanation / Answer
the F1 genotype is b+b/e+e. The gametes that F1 offspring produces have the following combination of the genotypes: b+e+, b+e, be+, be. Construct a Punnet square using the above 4 haploid genotypes for each parent and figure out the resulting 16 outcomes (4 X 4 = 16). Then figure out the phenotypes (color) using the information given in the exercise, namely only those organisms with homozygous alleles bb or ee will be black. if you do the accounting right, it should be 9 grey and 7 black.