In Drosophila , shaker ( sh ), bent ( b ) and twirled ( t ) are three recessive
ID: 54279 • Letter: I
Question
In Drosophila, shaker (sh), bent (b) and twirled (t) are three recessive genes. If homozygous shaker, bent females are crossed with homozygous twirled males, the resulting F1 progeny are all wild-type. If heterozygous F1 females are mated with shaker, bent, and twirled males, the following 1,000 progeny appear:
shaker, bent 371 Derive a map for the three (3) genes. (5 pt)
twirled 385
shaker, twirled 70
bent 75
wild-type 45
shaker, bent, twirled 38
shaker 5
bent, twirled 11
Explanation / Answer
Based on the given data,
So, the parental genotypes are as follows:
The genotypes of double cross over as follows:
There are 5 + 70 + 75 + 11 = 161 progeny show recombination between genes sh and b.
Thus, the gene distance between sh and b is 16.1 map units (m.u).
There are 45 + 38 + 5 + 11 = 99 progeny show recombination between genes b and t.
Thus, the gene distance between b and t is 9.9 (m.u), and the gene distance between sh and t is (16.1+9.9= 26 m.u).
From these sums it is clear that the “t/+” locus lies between the “sh/+” locus and the “b/+” locus.
Therefore, the genetic map of the three genes is as follows: