help with this genetic problem

Question

In drosophila, a trait called curled wing (cu) is recessive to a wild-type wing, a trait called striped body (sr) is dominant to wild-type body, and a trait called scarlet eye (st) is recessive to wild-type eyes. Scarlet mice with curled wings and a striped body were crossed to normal mice, and then the F1 mice were crossed to scarlet mice that have a curled wings and a normal body. The outcome of this cross was as follows:

Scarlet, curled, striped	560
normal eyes, normal wings, normal body	548
Scarlet, curled, normal body	102
Normal eyes, normal wings, striped body	104
Scarlet, normal wings, normal body	77
Normal eyes, curled, striped body	71
Scarlet, normal wings, striped body	11
Normal eyes, curled, normal body	9

1. What are the recombination frequencies between each of pair of genes?
2. Construct a genetic map that shows the order of these genes and distances between them

I did the problem but i would like to see if i actually did it together. I used the following: W= gene for wings; B= gene for body; and E gene for eyes; After doing the calculations I concluded 1) that gene W is the middle gene 2) distance between B and W is 11 mu 3) distance between W and E is 14 mu 4) distance between B and E is 25 mu. Is this correct or did I do something wrong?

Answer 1

Hello,

so the first thing we want to look at is figuring out what the parental classes are as there is no crossing over that occurs. We can tell by the groups that have the highest number are the parental classes. In this case it would be the Scarlet, curled, striped (560) and the normal eyes, normal wings, normal body with 548. In order to tell where the crossing over occurs, we look at the progeny with the lowest numbers. This means that the scarlet, normal wings, striped body (11) and the normal eyes, normal wings, and striped body (9) had crossing over events that are considered double.

The order of these genes are determined by looking at the parental vs the crossing over events. When we look at these we can see that the only thing that changed its position is the gene for wings. This means this should be the trait in the middle of the map. The order using your letters should be E-W-B.

The distance between eye color and wing is determined by:[ (77 +71+ 11 +9)/1482] *100. This means that the recombination factor is 11.34 map unit or cM (1 cM or 1 map unit is equal to the 1℅ of recombination frequency (RF) so the RF between St and cu is 11.34%.

The distance between the wings and the body type: [(no. of single cross over classes + no. of double cross over classes)/total no.]*100

=[ (102 +104+ 11 +9)/1482] *100

= 15.25 map unit or cM recombinant frequency between wings and body = 15.25 %.

Finally, to determine the distance between eye color and body: distance between eye color and wings + distance between wings and body

11.34 + 15.25 = 26.59 map unit or cM ( RF = 26.59%).

I hope this helps!!