In the cat, two gene loci on an autosomal chromosome are 32 map units from each

Question

In the cat, two gene loci on an autosomal chromosome are 32 map units from each other. At locus 1, the E allele for big ears is completely dominant to the e allele for small ears. At locus 2, the G allele for grey hair is completely dominant to allele g for white hair. A strain of cat, true-breeding for big ears and grey hair, is mated to strain 2, true-breeding for small ears and white hair. The F1 generation of that mating is mated with strain 2 (ie., a testcross) and 400 testcross progeny are produced.  

1. What is the expected frequency of gametes of genotype EG produced by the F1-generations cats? Show your calculations

2. When the F1-generation cats produce gametes, what is the expected frequency of gametes that have recombinant combinations of linked genes?

3. In the testcross progeny, how many cats are expected to have small ears & white hair? Show your calculations

4. In the testcross progeny, how many cats are expected to have small ears & grey hair? Show your calculations

5. If the two loci were not linked, and segregated independently from each other, how many cats are expected to have small ears & grey hair in the testcross progeny? Show your calculations

Explanation / Answer

It is given that, a strain of cat, true-breeding for big ears and grey hair (EEGG), is mated to strain 2, true-breeding for small ears and white hair (eegg). Cross between these two will have the offspring with the following genotypes.

EEGG* eegg = 100% EeGg. ---------> F1

Test cross of F1 is, EeGg* eegg = EeGg, Eegg, eeGg, eegg.

As genes E and G are separated by a distance of 32 map units, only 32% of the offspring are recombinant.

Means the frequency of Eegg and eeGg genotype = 32%, and the frequency of EeGg and eegg is = 68%.

Of the 68%, the frequency of EeGg genotype is 34%. The gametes produced by EeGg are 50% EG (34/2) and 50% eg (34/2).

Means the frequency of gametes of genotype EG produced by the F1-generations cats is = 17%.

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