Two pure-breeding strains of summer squash producing yel...

Question

Two pure-breeding strains of summer squash producing yellow fruit, Y₁ and Y₂, are each crossed to a pure-breeding strain of summer squash producing green fruit, G₁, and to one another. The following results are obtained:

Using clearly defined symbols of your choice, give the genotypes of parental, F₁, and F₂ plants in each cross.

Table showing crosses of summer squash with genotypes and phenotypic ratios.
Using clearly defined symbols of your choice, give the genotypes of parental, F₁, and F₂ plants in each cross.

Accepted Answer

Hi, everyone. Welcome to the next problem. It says two pure breeding strains of a plant designated P one and P two produce flowers of the same color, which is purple. Each of these strains when crossed with a pure breeding strain X produces F one progeny plants that have pink flowers when pure breeding P one and P two are crossed. The F one progeny plants have pink flowers and self fertilization of the F one prone resulted in 9/16 plants with pink flowers and 7/16 plants with purple flowers determine the genotype of the parents of the F one progeny. And our answer choices are a big, a big, a big B big B crossed with big A big, a little B little B choice B little, a little A big b, big B crossed with big A big, a little B little B choice C big A little A big B little B cross with big, a little A big B little B and choice D little A little A little B little B cross with big A big, a little be little be. So this plant, this question, there's a lot of information at us. So let's try and kind of organize it. So we have three strains that we look at. We have P1, P two and X & P 1 and P two. We know produce purple flowers and we know they must be homozygous because they're true breeding then strain ax. We don't know what color of flowers it produces, but it also must be homozygous. And we know that when P one or P two are crossed with X, the F one progeny plants are all pink. And we know by looking at our answer choices that we have two genes involved here. So that would lead us to the idea that we have an epis static interaction. We have the expression of a second gene affecting the expression or masking the expression of the first one. In this case, we see that strain X must be the sort of overriding factor here since P one and B two are both purple when left alone, since X must be homozygous, and we see it sort of overriding the other genes we're gonna posit that it must be homozygous dominant in both genes A and B, which is what causes it to sort of override the phenotype of the other types. So then with P one and P two, we need something that could be homozygous and result in two different genotypes giving the same phenotype. Well, we can do that if they each are homozygous dominant in one gene and homozygous recessive in the other. So if we say P one is big, a big, a little B, little B MP two is little, a little, a big B, big B. So this would kind of give us a scenario where if we have two dominant all, so a dominant allele in either gene as we have with X where we've got big A and big B that leads to that pink color. But if we have only one dominant, all, so at least one of the genes is homozygous recessive, we get purple and that lets us have those two different genotypes for P one and P two. But they each have one of their genes, homozygote being homozygous recessive. And now our question asks us, what's the genotype of the parents of the F one progeny? Which is a result of a cross between P one N P two that gives us F one progeny that have pink flowers. Well, if we theorize that having one dominant ally from each gene results in the pink phenotype, we know P one and P two must be homozygous, then we can posit that P one would be big. A big, a little B, little B while P two is little, a little A big B, big B. In this case, each strain has only one dominant alley and they have two different genotypes, but both will produce purple flowers as they have one gene. Still in the homozygous recessive state and the offspring of this cross will inherit a big A a from one parent with a little A, a from the other. And then big B from one parent and little B from the other. So they will be heterozygous for both traits. This makes sense with our uh our observation that self fertilization of this F one progeny results in 9/ plants with pink flowers and 7/16 plants with purple as that 9 to 7 ratio is characteristic of a die hybrid cross as that cross would be where there is complementary gene interaction like our episodic interaction here. But here we're asked for the genotype of appearance of the F one progeny. And that would be the genotype of strains P one and P two. So we have big A big, a little B, little B, little, a little A big B, big B and we see that cross here in choice B. See you in the next video.

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