In the rats identified in Problem 10, a third independen...

Question

In the rats identified in Problem 10, a third independently assorting gene involved in determination of coat color is the C gene. At this locus, the genotype C– permits expression of pigment from genes B and D. The cc genotype, however, prevents expression of coat color and results in albino rats. For each of the following crosses, determine the expected phenotype ratio of progeny.

BbDDCc×BbDdCc

Accepted Answer

Hi, everyone. Welcome back. Here's our next problem. Assume that black, short hair, big be big B big S big S is dominant in guinea pigs over white long hair. Little be little B little s little S heterozygous black, short guinea pigs. Big B little B big S little S are produced in the F one generation. When the genotype Big B big B big S big S crosses with little B little B little s little S, what would be the phenotypic distribution of the F two generations offspring if these F one hybrids are interbred and our answer choices are a nine white short guinea pigs, three black long guinea pigs, three black, short guinea pigs, one white, long guinea pig choice B, nine black, short guinea pigs, three black long guinea pigs, three white, short guinea pigs, one white long guinea pig choice C three black short guinea pigs, one white long guinea pig and D none of these. Well, when we have a cross between two heterozygote as we do here, we know our F one generation are heterozygous for both traits and that we've interbred them. So our cross that's going to produce the offspring we're looking at it's heterozygous for both traits, put that there, that's a die hybrid cross. And it's always convenient to remember the phenotypic ratio that you expect from a dye hybrid cross like this. And that would be 21 where the nine expresses both dominant traits. And then the threes express individuals that are dominant for one trait and recessive for the other. And then the one is recessive for both traits. So as we look at our answer choices before we even look at which being a type combinations will be, which we can eliminate choice C because it says three black short and one white long. So that doesn't even correspond with our expected 9 to 3 to 3 to 1 ratio. So choice C is not there. So we've got two options A and B with the correct numbers here. So let's look at and evaluate the phenotypes and see which matches. So both dominant traits in this case will be black short. So the nine expected offspring should be black and short fur. And in choice B I see that that is the case, I can eliminate choice A because it has 9 White short. So choice A is not going to be our answer. Let's keep looking at choice B and make sure it matches correctly because I do have that possibility in choice B that none of the answers are correct. So I need to check all of the phenotypes here. The next is the three black long. Well, that is indeed, we'd expect this to be one dominant and one recessive trait, the black fur is dominant. The long fur is recessive. So that checks out and next is three white, short guinea pigs. The white fur is recessive and the short fur is dominant. So that's again, one recessive and one dominant and finally one white long, which is both recessive traits. So we have our correct answer in choice. B we can eliminate choice D, none of the above or none of these. And our phenotypic distribution of the F two generations offspring. If this, the F one hybrids are interbred, this choice be nine black, short guinea pigs, three black long guinea pigs, three white, short guinea pigs and one white long guinea pig. See you in the next video.

Key Concepts

Independent Assortment

Genotype and Phenotype

Epistasis

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