A kidneybean shaped eye is produced by a recessive gene, k, on the third chromos

Question

A kidneybean shaped eye is produced by a recessive gene, k, on the third chromosome of Drosophila. Orange eye color, called cardinal, is produced by the recessive gene cd on the same chromosome. A third recessive gene on chromosome three, e, produces ebony body color. Trihybrid females are testcrossed to produce 4000 progeny, as follows:

1761    kidney, cardinal

1773    ebony

128      cardinal

97        kidney

89        ebony, cardinal

6          kidney, ebony, cardinal

8          wild type

138      kidney, ebony

            a. Which gene is in the middle?  

            b. What is the distance between genes k and cd?

            c. What is the distance between genes e and k?

            d. What is the distance between genes cd and e?

Explanation / Answer

Total nubmer of progeny = 1761+1773+128+97+89+6+8+138 = 4000

Frequency of gene k = 1761 + 97+ 6 + 138 = 2002 / 4000 = 0.50

Frequency of cardinal = 1761 + 128 + 89 = 1978/4000 = 0.49

Frequency of ebony = 1773 + 89 + 6 + 138 = 2006/4000 = 0.51

The gene k is situatedin the middle.

The distance between genes k and cd = (050 - 0.49) = 0.01m.u

The distance between genes e and k = (0.51 - 0.50) = 0.01m.u

The distance between genes cd and e = (0.51 - 0.49 ) = 0.02m.u

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