Imagine you have identified three X-linked genes in Drosophila . Recessive mutat

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?

A.   __________________ and __________________

B. Diagram of P1 Cross

:

Diagram of F1 Cross:

C. Chromosome map (horizontal; top of chromosome at left):

D. ___________________________________________________________________________________________________

E.____________________________________________________________________________________________________

Explanation / Answer

From the given information, it can be seen that the order of the genes is a b d. If the parent 1 is a b + and parent 2 is + + d. The genotype of F1 parents is a b + / + + d

The following is the result of offspring genotypes:

A. The most closely linked genes are beta and delta

B. The genotypes are as follows:

Parent male: delta wings, normal eye and body color: + + d

Parent female: alpha body, beta eye: a b +

F1 progeny genotype: a b + / + + d

D. Males are hemizygous for X chromosome and hence, hemizygous for the x chromosome. They contain either of the traits only.

Related Questions

Navigate

• Browse (All)
• Browse I
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.