A true-breeding wild-type female fly with a gray body and long bristles is cross

Question

A true-breeding wild-type female fly with a gray body and long bristles is crossed to a true-breeding male fly with an ebony body and short bristles. Then, a test cross is conducted in which F1 heterozygous females are crossed to true-breeding male flies with ebony bodies and short bristles. The ebony (e+) and short (s+) genes are linked. A. For the test cross, list the genotypes of all possible female gametes and all the possible male gametes if no crossing-over occurs. B. What additional female gametes are obtained through crossing over? C. The progeny of this cross are described in the chart below. Calculate the distance between the ebony (e+) and short (s+) genes. Show all of your calculations. Gray Body, Long Bristles: 447; Ebony Body, Short Bristles: 453; Gray Body, Short Bristles: 52; Ebony body, Long Bristles: 48

Explanation / Answer

Female e s X e+ s+ Male

F1          e s
           e+ s+

Test cross

female            e s    X    e+ s+ Male
                 e+ s+       e+ s+

A. Gametes

Female gametes   e   s    gray body and long bristles
                     e+ s+     ebony body and short

Male gametes    All gametes are e+ s+ ebony body and short

B. Crossing over

Female gametes   e s+ gray body and short
                  e+ s   ebony and long

C.

     Distance = 52 + 48 / 1000
              = 100 / 1000
              = 0.1 cM

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