Imagine you have identified three X-linked genes in Drosophila . Recessive mutat
ID: 54811 • Letter: I
Question
Imagine you have identified three X-linked genes in Drosophila. Recessive mutations in these genes result in either alpha body color (a); beta eye color (b), or delta wing shape (d). An alpha bodied, beta-eyed female with normal wings was crossed to a male with delta wings but normal eye and body color. F1 females were wild type for all three traits; F1 males had alpha body and beta eye colors. When F1 flies were mated with each other, the following results were obtained
(Note that only male F2 flies were counted):
Male F2 flies with phenotypes noted:
alpha, delta 8
beta 7
alpha, beta, delta 94
wild type 91
delta 380
alpha, beta 420
alpha 0
beta, delta 0
A. Which two genes are most closely linked?
B. Diagram (using double lines for homologous chromosomes and standard genetic symbols for males and females) the genotypes of the P1 and F1 flies used in these crosses.
C. Draw a map that shows the estimated location of each gene on the X chromosome. Assume the beta gene was already mapped to position 2.0 cM, close to the top of the X chromosome.
D. Why were two phenotypes listed above not found among male flies in the F2 generation?
E. When a friend recommends that you cross your delta mutant with the well-characterized cut (ct) wing mutant of Drosophila, you find that the two mutants fail to complement. What can you conclude from these results?
Explanation / Answer
1. most closely linked genes could be beta and delta as there is no recombination.
2. Parents: dd* aabb
F1 used for the cross: dab*dab
3. map position of the three genes: delta - alpha -beta
4. the not found phenotypes are mostly due to they donot move together
5. If they fail to complement means the delta allele is not from the same gene as that is from the cut wing allele.
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