You just bought two black guinea pigs one male and one femal

You just bought two black guinea pigs, one male and one female, of the same genotype from the pet store that are known to be heterozygous (Bb). You also know that black fur (BB) is dominant over white fur (bb), and that a lethal recessive allele is located only one cM away from the recessive b allele and your animals are both heterozygous for this gene also. You decide to start raising your own guinea pigs, but after mating these animals several times, you discover they produce only black offspring among the first 12 progeny. How would you best explain this result? The B locus is on the X chromosome, so it can never produce a white phenotype. The B allele is actually codominant with the b allele, so a white phenotype cannot be produced. The recessive I allele is in tight coupling linkage with the b allele, so almost all of the bb offspring will also be II and thus die before they can be observed. The dominant L allele is in tight repulsion linkage with the B allele, so it will be impossible to produce the Bb genotype that would express the white phenotype. Normally, it would be expected that 25 percentage of the offspring would be white, but in this case, random deviations from the expected resulted in no white offspring.

Solution

The most appropriate choice is option c.

For a guineapig to be white, it must have the bb genotype. Both Bb and BB genotypes would be black. Now. the b allele is closely linked to the lethal l allele. So, every white guinepig (bb) would also very likely be homozygous for the lethal l allele (ll) and hence dye. Thus, upon breeding we get only black individuals (BB, LL; Bb, Ll).