In Drosophila, a female fly is heterozygous for three autosomal mutations, apric
ID: 6946 • Letter: I
Question
In Drosophila, a female fly is heterozygous for three autosomal mutations, apricot eyes (a), fused bristles (f), and lobe wings (L). This heterozygous female was testcrossed. The results of the testcrossed are shown below:
apricot
49
fused, lobe
51
fused
198
apricot, lobe
202
lobe
52
apricot, fused
48
wild
200
apricot, fused, lobe
200
Prior to obtaining the above results you crossed a true-breeding female with apricot eyes, fused bristles, and lobe wings to a true-breeding wild-type male. All F1 males and females had lobe wings.
I am aware that apricot eyes and lobed wings are linked, but am unable to determine why the distance between the genes is 20.
Please give a detailed explanation of the recombinants in the problem and which of the results are used to determine the gene map.
Explanation / Answer
Given that,
apricot 49
fused, lobe 51
fused 198
apricot, lobe 202
lobe 52
apricot, fused 48
wild 200
apricot, fused, lobe 200
Total progeny = 1000
The recombination frequency between the apricot and fused genes are
= 49+51+198+202 = 500 / 1000 = 0.5
The recombination frequency between the fused and lobed genes are
= 108+20+52+48 = 410 / 1000 = 0.4
The recombination frequency between the apricot and lobed genes are
=49+51+52+48 = 200 /1000 = 0.2
The map distances between the genes is
apricot---------0.2--------lobed------------0.4-------------fused
<-----------------------------0.5-------------------------------------->
These results are obtained from the cross between apricot eyes, fused bristles and lobed wings female crossing with wild recessive male. The genes responsible for apricot eyes and lobed wings are linked as all the F1 progeny have lobed wings.