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How to find parents' genotypes from progeny phenotype frequencies?

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visharad
#1
Sep15-11, 06:37 AM
P: 53
Question: 8 phenotypes were observed as a result of a trihybrid cross. The frequencies of the phenotypes are

a+ b+ c- = 570
a- b- c+ = 545
a+ b- c+ = 17
a- b+ c- = 20
a+ b- c- = 140
a- b+ c+ = 128
a+ b+ c+ = 65
a- b- c- = 61

No other information is given. It is not even specified if it is a testcross. How to know if the genes were linked? Also, what are the possible genotypes of the parents?

My attempt - The phenotypes with the two largest frequencies represent parental classes. Thus a+ b+ c- and a- b- c+ are parental recombinant phenotypes.
The phenotypes a+ b- c+ and a- b+ c- are double recombinant phenotypes as these have the smallest frequencies. The other 4 are single recombinant phenotypes.
But I do not know how to proceed from here.

Suppose I calculate the % of all the recombinant (single and double) phenotypes and find it to be less than 50%, can I conclude that the genes were linked?
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