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 3 cM (3 centimorgan) 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 produce only 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’d expect to see a white guinea pig?

c. Indicate the most likely genotype of the white offspring.

Explanation / Answer

Answer:

a. The recessive lethal allele is tightly linked to, and thus co-segregates with, the recessive allele, which is lethal in the homozygous state (bb).

b. 1% of the gametes will be recombinant (Bl or bL)

0.5% of the gametes will be Bl

0.5% of the gametes will be bL

white animals can have the following genotype:

genotype probability

bL/bL (0.005)(0.005) = 0.000025

bl/bL (0.495)(0.005) = 0.002475

bL/bl (0.005)(0.495) = 0.002475

the probability of white animal =0.004975

1/0.004975 = 201

therefore on average, you’d have to look at 201 progeny before seeing a white animal so on average you’d have to do 21 matings.

c. The white offspring would most likely have the genotype bL/bl.

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