Below, there are two genetic maps each based on testcross data collected from di

Question

Below, there are two genetic maps each based on testcross data collected from different matings between different strains of mice. Strain 1, the tester, was homozygous for recessive alleles at each locus on the map.   Strain 2 mated with strain 3 and then their F1 was mated to strain 1 to produce the testcross progeny and map 1. Strain 4 mated with strain 5 and then their F1 was mated to strain 1 to produce testcross progeny and map 2.

Based on the genetic map, which F1 (2x3 or 4x5) was most likely to be heterozygous for a pericentric inversion for the homologs that carried the gene loci on the map? Briefly, and legibly, explain your choice:

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Explanation / Answer

The pericentric inversion is the inversion of chromosome occurring in two arms of chromosome including the centromere. The strain 1 is homozygous recessive for each locus. The map 1 is produced by F1 offspring resultant of cross between strain 2 and 3 that are test crossed to strain 1. The map 2 is produced by F1 offspring resultant of cross between strain 4 and 5 that are test crossed to strain 1. Basing on the genetic map the strain 4x5 was most likely to be heterozygous for a pericentric inversion for the homologs that carried the gene loci on the map. This is because, the map 1 and map 2 are similar at all loci except between b and c. In map 2, between b and c the number of alleles is only 3. The 3 alleles can be homozygous dominant, recessive resulting in a heterozygous genotype. If the given locus contains 1 dominant and 2 recessive there is a chance of 50% heterozygous offspring. If the given locus contains 2 dominant and 1 recessive, there is a 50% chance of heterozygous offspring. Therefore, the cross between strain 4 and 5 resulting F1 offspring test crossed to strain 1 producing map 2 is heterozygous for the locus 3.

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