The linkage of three genes affecting coat color in mice were studied: mahogany (
ID: 33807 • Letter: T
Question
The linkage of three genes affecting coat color in mice were studied: mahogany (mg), agouti (a) and ragged (rg). A series of three point crosses were carried out, in which mice that were heterozygous at all three loci were mated with mice that were homozygous for the recessive alleles. The table below lists the results of the testcrosses. Note that a + designates the wild-type allele. Using this information, what is the order of the genes on the chromosome, and what are the map distances between the three loci?
Explanation / Answer
The linkage relations of three genes affecting the coat color in mice were studied. The three coat colors are mahogany (mg), agouti (a) and ragged (rg). A series of three point crosses were carried out, in which mice that were heterozygous at all three loci were mated with mice that were homozygous for the recessive alleles at these loci.
The results of the test cross are as follows:
Phenotype
Number
a Pg +
1
+ + mg
1
a + +
15
+ Pg mg
9
+ + +
16
a Pg mg
36
a + mg
76
+ Pg +
69
Total
213
Based on the numbers of progeny,
Non-recombinants = a + mg, + Rg +
Double crossovers = a Rg +, + + mg
These phenotypes differ in the locus
Phenotype
Number
a Pg +
1
+ + mg
1
a + +
15
+ Pg mg
9
+ + +
16
a Pg mg
36
a + mg
76
+ Pg +
69
Total
213
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