Calculating % recombination and Mapping distance

[gymgrl]

Hey,


Im confused on how to caluclate the percent recombination and the the mapping distznce in map units. Heres my problem:


Consider a cross in Neurospora involving two allelles at the same locus,C and c. The following tetrad patterns were observed


CCcc 55
ccCC 40
CcCc 7
cCcC 3
CccC 4
cCCc 5

What is the percent recombination and the approximate distance between the genetic locus and the centromere is?
I can't calcualte my percent recombination because im unsure jof the significant difference. But I clacuated my mapping distance by: Getting the sum of all my numbers which is 114,then I added the 4 smaller numbers and I got 19. Now for my calcualteions

19/114=0.166 then divide by 2 since its two genotpyes that are CC and cc.
which equals 0.083,then I multiply by 100 which give me 8.33 mapp units.


But How do I find my percent recombination from my data?
Are there seperate equations for percent recombination and the mapping distance?
Thank you ttyl

[mith]

I don't think you should divide by 2, map distance is of total recombinations.

[Cat]

You calculated everything correctly. 8.33 m.u. is also = to 8.33 % which is recombination frequency (1% RF= 1 m.u.).

Your reasoning is not correct though (unless I misunderstood you). You said “19/114=0.166 then divide by 2 since its two genotypes that are CC and cc.”

0.166… or 16.6% is frequency of crossover during meiosis, but only ½ of the product is recombinant. That is why you have to divide by 2; RF = 1/2 of the frequency of crossover during meiosis in this case.