Q2. In Drosophila, wild-type eye colour is red and wild-type wings are long. A f
ID: 205194 • Letter: Q
Question
Q2. In Drosophila, wild-type eye colour is red and wild-type wings are long. A female fly pure-breeding for brown eye (with wild-type wings) was crossed to a male fy pure breeding for short wings (with wild-type eyes). The F progeny were all wild-type. Two F, flies were then crossed, and produced the following F2 generation: Wild-type Brown Short Brown, Short Total 178 62 56 24 320 Produce a diagram of the cross that explains these results. Include the genotypes and phenotypes for all three generations. Use the symbols b for brown eyes and b* for wild-type eyes, s for short wings and st for wild-type wings. Indicate the dominance relationship between alleles. (How do you know?)Explanation / Answer
Answer:
Female, brown eye, wild-type wings (bb s+s+) x Male, short wing, wild-type eyes (ss b+b+)---P1
b+b s+s --------------------------------------------------------F1 (wild-type eyes & wild-type wings)
b+b s+s X b+b s+s ---F1 x F1
b+s+
b+s
bs+
bs
b+s+
b+b+ s+s+ (wild-type)
b+b+ s+s (wild-type)
b+b s+s+ (wild-type)
b+b s+s (wild-type)
b+s
b+b+ s+s (wild-type)
b+b+ ss (short wings)
b+b s+s (wild-type)
b+b ss (short wings)
bs+
b+b s+s+ (wild-type)
b+b s+s (wild-type)
bbs+s+ (brown eyes)
bbs+s (brown eyes)
bs
b+b s+s (wild-type)
b+b ss (short wings)
bbs+s (brown eyes)
bbss (brown eyes & short wings)
Wild- type = 9/16
Brown = 3/16
Short = 3/16
Brown, short = 1/16
The above cross clearly shows as dihybrid cross. The phenotypes that were expressed in F1 are the dominant phenotypes of their respective genes.
Red (wild-type) eye is dominant over brown eyes.
Long (wild-type) wing is dominant over short wing.
b+s+
b+s
bs+
bs
b+s+
b+b+ s+s+ (wild-type)
b+b+ s+s (wild-type)
b+b s+s+ (wild-type)
b+b s+s (wild-type)
b+s
b+b+ s+s (wild-type)
b+b+ ss (short wings)
b+b s+s (wild-type)
b+b ss (short wings)
bs+
b+b s+s+ (wild-type)
b+b s+s (wild-type)
bbs+s+ (brown eyes)
bbs+s (brown eyes)
bs
b+b s+s (wild-type)
b+b ss (short wings)
bbs+s (brown eyes)
bbss (brown eyes & short wings)
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