A stock homozygous for three recessive autosomal genes: a, b, andc, not necessar

Question

A stock homozygous for three recessive autosomal genes: a, b, andc, not necessarily linked on the same chromosome, is mated to astock homozygous for their dominant wild-type allele. F1 femalesare then backcrossed to males of the homozygous recessive parentalstock and the following cross results are observed:

Phenotype        Number
a bc                    42
+ ++                    48

a ++                    46
+ bc                    44

a b+                      6
+ +c                      4

a +c                      5
+ b+                      5


1. Which of these genes are linked?


2. What is the recombination frequency between linked genes?




(Note: sorry for re-posting but I really need the answer and when Ichecked my previous post the format was messed up, but look on thebright side, If you get it right twice you get double karmapoints)

Explanation / Answer

1. These data fit the pattern for two loci linked, oneunlinked. Looking at the genotypes, the for smaller classes eachhave recombinant combinations for b and c, but not for the othercombinations (a vs. c, or a vs. b). Hence, b and c are linked, anda is on another chromosome.

2. r(bc) = (6+4+5+5)/(6+4+5+5+42+48+46+44) = 0.1

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