16. In Drosophila, Dichaete (D) is a mutation on chromosome III with a dominant

Question

16. In Drosophila, Dichaete (D) is a mutation on chromosome III with a dominant effect on wing shape. It is lethal when homo- zygous. The genes ebony body (e) and pink eye (p) are recessive mutations on chromosome III. Flies from a Dichaete stock were crossed to homozygous ebony, pink flies, and the Fi progeny, with a Dichaete phenotype, were backcrossed to the ebony, pink homozygotes. Using the results of this backcross shown in the table, (a) Diagram this cross, showing the genotypes of the parents and offspring of both crosses. (b) What is the sequence and interlocus distance between these three genes? Phenotype Dichaete ebony, pink Dichaete, ebony Number 401 389 84 96 in Dichaete, pink ebony ichaete, ebony, pink wild type 12

Explanation / Answer

a)Represent the dichaete gene as an uppercase letter because it is dominant.At this point, the gene sequence is not given:

P1: D+ +/+ + *+ e p/+ e p

F1: D+ +/+ e p * + e p/+ e p

F2: D+ +/+ e p Dichaete

+ e p / +e p ebony, pink

D e +/ + e p Dichaete, ebony

+ + p/+ e p pink

D + p/+ e p Dichaete , pink

+ e +/+ e p ebony

D e p/+ e p Diachete, ebony, pink

+ + +/+ e p wild type

b) F1: D + +/+ p e * + p e/ + p e

D-p=3.0 map units p - e = 18.5 map units.

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