A male and a female mouse are each from pure-breeding al...

Question

A male and a female mouse are each from pure-breeding albino strains. They have a litter of 10 pups, all of which have normal pigmentation. The F₁ pups are crossed to one another to produce 56 F₂ mice, of which 31 are normally pigmented and 25 are albino.

What genetic phenomenon explains the F₂ results? Use your allelic symbols to explain the F₂ results.

Accepted Answer

Hi, everyone. Let's look at our next problem. It says what is the fanatic ratio of a hetero ziggy's cross in recessive episode? Asus? Well, episode Asus is when we see the interference of a gene in one locus with the expression of a gene and another locus. And in this case, we have recessive episode Asus. So what is happening there when a home, a sickness recessive genotype at one locus masks the expression of a dominant allele at a second locus. So we imagine a scenario where we have genes A and B and we're going to say in this case, the genotype Little B, Little B masks the expression of big A. So how will this express the, how will this affect the phenotype ratio of heterosexuals cross? Well, we know that normally when we have two different genes, some individuals, parents who are heterosexual at both genes are di hybrid cross that are expected in a typical ratio of the offspring will be nine. I'm gonna write this vertically rather than horizontally, 9-3-3-1 where the nine is going to be expressing both dominant traits. So, in the phenotype again, we remember. So no matter what the genotype is, the traits expressed dominant trait for a dominant trait. For b, then three will be one dominant, one recessive, Then three will be other way around one dominant or one recessive, one dominant. And then the one will be both recessive traits being expressed. And again, we'll think about the Jenna types, reflecting each of these phenotype Cina di hybrid cross and recall these Jenna types will be the same. Even in the case of recessive episode Asus, it will be the fanatic expression that will be affected. So when in the nine here, when both dominant traits are expressed in the phenotype, the genotype will be big a blank, Bigby blank. We know we have one dominant allele of each trait. But the second Aliyah can be either dominant or recessive or three. Here, one dominant, one recessive will have dominant allele A and then blank and then be well expressed the recessive trait for B. So that would be little B little B, the next three would be flipped. So we've got little a little A one big B and then blank for the second value. And finally, both recessive traits, the one would be little a little, a little B little B. So now how does are the presence of recessive episode Asus affect the phanatic ratio? Well, we've said that it means that little B little B, if B is homocide is recessive, it masks the expression of dominant allele A. So let's look at our nine that remains unchanged because we have one dominant llB. So dominant L A can be expressed just fine. So this will still be nine, both dominant traits being expressed. Now, let's look at the three. Well, we've got dominant allele a and then little B, little B were homos, I guess recessive for B that's going to mask the expression that dominant A. So instead of expressing the dominant A recessive B, both traits expressed will be recessive because that dominant A trait will be masked. Then let's go to the next three. Here. We have little, a little A and then big B blank. Well, this will remain the same. You're going to have one recessive, one dominant because the little A little A does not mask B. This is not to genes interacting with each other. This is the effect of JEAN B and the recessive recessive condition on gene A. So in this case, you've got your big B and it's not affected by the homos, I guess recessive A and finally, both recessive traits. Little a little a little B, little B, no change there. You still got your one, both recessive. So now we have still have three that express one recessive and one dominant from the case, we had a little, a little A but we don't have the other three. Those three are now expressing both recessive traits. So combined with our original one we have three plus one expressing both recessive traits. So let's look at our final fanatic ratio here For both dominant traits being expressed, we have nine. Still then for one dominant one recessive, we now only have three. And then finally, for both recessive being expressed, we have four. So our ratio fanatic ratio that will expect to see when there's recessive episode basis going on. It will be choice C 9 to 3 to four. See you in the next video.

Key Concepts

Mendelian Inheritance

Punnett Square

Allelic Symbols

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