In Drosophila purple eyes are recessive to red eyes, and miniature wings are rec
ID: 5750 • Letter: I
Question
In Drosophilapurple eyes are recessive to red eyes, andminiature wings are recessive to normal wings. Apure breeding red-eyed, normal-winged fly iscrossed with a pure breeding purple-eyed,miniature-winged fly. An F1 female is crossedwith a male that has purple eyes andminiature wings. The following progeny areobtained:74 red, normal 20 red, miniature 28 purple, normal 78 purple, miniature
Are the two genes, linked? If so, how many map unitsseparate them? In Drosophilapurple eyes are recessive to red eyes, andminiature wings are recessive to normal wings. Apure breeding red-eyed, normal-winged fly iscrossed with a pure breeding purple-eyed,miniature-winged fly. An F1 female is crossedwith a male that has purple eyes andminiature wings. The following progeny areobtained:
74 red, normal 20 red, miniature 28 purple, normal 78 purple, miniature
Are the two genes, linked? If so, how many map unitsseparate them?
Explanation / Answer
Sometimes, the autosomal genes are not inherited according tothe 9:3:3:1 Mendelian ratio for two independently assorting genes.For the question, the body color and shape of fly are autosomalgene. The parental classes and therecombinant classes are not present in the same ratio 1:1;1:1;indicate that the genes are linked. We also can carryout the test cross to see whetherthe the genes are linked or not linked as well.First, we let red=R+, purple=R, normal wing=N+, miniature=N
so, 74R+N+ 20 R+N 28 RN+ 78 RN The parental combinations are R+N+ and RN while the recombinantsare R+N and RN+. Thus, to calculate the R and N distance, calculateas the percentage of recombinants in the total number of progeny,is
(20+28)/200 x 100=24 m.u so, the genetic distance between this two gene is24m.u.