You just bought two black guinea pigs from the pet store that are known to be he

Question

You just bought two black guinea pigs 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.You decide to start raising your own guinea pigs, but after mating these animals several times you discover they only produce black progeny.

a.How would you explain this result?

b.If the original black guinea pigs produce an average of 10 offspring per mating, how many matings would you have to make before you

Explanation / Answer

a. The recessive allele is b, we can say that white fur (which was homozygous recessive, bb) alleles slowly mutated to lethal allele. This resulted in black fur since it could be BB or Bb. The 1/4 prgeny carrying bb died while the heterozygotes which were Bb survived and produces black progeny due to the recessive nature of lethal allele. Since the distance given is only one cM it can be implied that all the b changed to lethal alleles.

b. Originally the cross would have produced 75% black and 25% white fur progeny. So in the first mating 25% of 10 offsprings would be expected to be white offsprings.

c. Since the white phenotype is produced in the absence of dominant B, hence, it is bound to be homozygous recessive. Therefore, the most likely genotype for white fur would be bb.

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