In Drosophila echinus eye colore is recessive to wild type e

In Drosophila, echinus eye color(e) is recessive to wild type eyes (e+), crossveinless wings (c) is recessive to wildtype wings (c+), and scute bristles (s) is recesive to wild type bristles (s+).Two pure true-breeding strains of flies are crossed to generate F1 offspring that are heretrizygous for all three genes with wild phenotype. The testcrosses were performed using female F1 flies to male flies with echinus, crossveineless wings and scute bristle. The progeny of this testcross are:

Solution

Wild type eye e+, recessive echinus eye e

Corssveinless wings recessive c

Scute bristles recessive s

Offspring genotype = e+e s+s c+c

Test cross between female F1 offspring and male ee ss cc

ee= 8576

ss= 977

cc= 716

eess= 681

cc ss = 8808

cc ee ss=4

cc ee =1002

e+e s+s c+c = 3

Single cross over progenies always greater than double crossover

The least progenies are telling that they are produced through double crossover.

Genotypes ss, cc, eess, and ccee are produced by single cross over, so the gene order is c e s

Single cross over between c and es, frequency = [716+ 681+4+3/ 20767] x100 = 0.069 x100 = 6.9cM

Single cross over between ce and s = [ss + ccee + double crossover/ total progenies] x100

= 977+1002+4+3/20767 ] x100 = 0.096 x 100 =9.6 cM

So map would be

c----6.9cM---e---9.6cM----s