Three strains of green-seeded lentil plants appear to have the same phenotype. The strains are designated G₁, G₂, and G₃. Each green-seeded strain is crossed to a pure-breeding yellow-seeded strain designated Y. The F₁ of each cross are yellow; however, self-fertilization of F₁ plants produces F₂ with different proportions of yellow- and green-seeded plants as shown below.
For what number of genes are variable alleles segregating in the G₁ x Y cross? The G₂ x Y cross? In the G₃ x Y cross? Explain your rationale for each answer.

Question

Three strains of green-seeded lentil plants appear to have the same phenotype. The strains are designated G₁, G₂, and G₃. Each green-seeded strain is crossed to a pure-breeding yellow-seeded strain designated Y. The F₁ of each cross are yellow; however, self-fertilization of F₁ plants produces F₂ with different proportions of yellow- and green-seeded plants as shown below.

For what number of genes are variable alleles segregating in the G₁ x Y cross? The G₂ x Y cross? In the G₃ x Y cross? Explain your rationale for each answer.

Table showing F1 and F2 phenotypes of green-seeded lentil strains G1, G2, G3 crossed with yellow strain Y.

For what number of genes are variable alleles segregating in the G₁ x Y cross? The G₂ x Y cross? In the G₃ x Y cross? Explain your rationale for each answer.

Accepted Answer

Hi, everyone. Welcome back. Let's look at our next question. It says, what is the fanatic ratio of a hetero zegas cross in a complementary gene interaction? Let's recall what a complimentary gene interaction is agena interaction is when you have genes that two or more different lo sai and the expression of one gene has some sort of interfering effect on the expression of the other gene. In this case, we have a complementary gene interaction. And that means that you need at least one dominant allele of each gene to express a particular phenotype. Meaning if either alil is present in the recessive homogeneous condition, this masks the expression of the dominant allele at the other locus. So let's look at what this means we know that usually when we have a di hybrid cross, two different genes and two heterocyclic, it's cross together that we end up with a fanatic ratio. I'm gonna write it in a vertical fashion of nine, 2, 3, 2, 3, 2 1, the nine being dominant in both traits. It's a dominant, both. And let's remember there's a fanatic ratio. So that would mean both traits are expressed in the dominant phenotype then three, one dominant trait, one recessive trait, the other three being one recessive, one dominant. So the opposite combination and the one being both recessive traits being expressed. So that's it. There's no gina interaction. Now, when there's complimentary gene interaction, we need to look at and think about what the genotype is in each of these fanatic pick um expressions that we have. So in our 9 to 3 to 3 to 1 ratio, the nine representing both dominant traits being expressed, um We're gonna call our genes A and B. In this case, that would mean there's at least one big A one dominant allele. The second could be either one, right? Because it's a dominant gene. And then, so we're big a blank and then big B blank again, one dominant allele, the other one can be either way. Then in the case of the first three, in that peanut ipic ratio, one dominant, one recessive. Well, gene A will be dominant so big A and then blank. But then gene B is going to express the process of phenotype. So that will be little B, little B. The next three is recessive and dominant. But the other way around. So gene A is recessive, so little a little A and then B will have one big B and then blank because the other gene can be the other alley can be either one. And then finally, when both recessive traits are expressed, we know that must be little, a little, a little b, little B. So those are our genotype ratios. So now let's consider them in the case of complementary gene interaction, we know that that means if there's either a little present in a recessive homosexuals condition, it's going to mask the expression of the dominant allele of the other gene. So in case of the nine, we have both genes present and with at least one dominant allele. So in this case, we still will express um both dominant traits, there's no masking going on. So this will still be nine expressing both dominant traits. In the case of complementary gene interaction, say that's on that side, this side is no gene interaction. On the left side, it's our 9 to 3 to 3 to 1 ratio. And then on the right here, I'm writing complimentary gene interaction. Now we look at the three with no gender action which we know we have little B little B, we have that in the homesickness recessive. So that little B, little B is going to mask the expression of the dominant A. So we're going to end up seeing both recessive traits being expressed since the dominant A trait will be masked by the recess that homesickness recessive B. Now let's look at the next three that has little a little A and then big B blank. Well, again, having homesickness recessive A will mask the expression of JEAN B in this case. So both recessive traits will be expressed in the phenotype with that big B being masked. And then of course, the one will be unchanged. Two recessive traits will show both recessive traits in the phenotype. So now when we look the three, the three and the one from our original ratio, all now express both recessive traits. So we have three plus three plus one equals seven Out of the 16 total offspring possibilities being both recessive traits being expressed in the phenotype. So we have no more option for one dominant, one recessive trait to be expressed. And we see a ratio of 9-7 where nine is both dominant traits being expressed in the phenotype and seven is both recessive traits being expressed. So let's look at our answer choices and the choice d is 9-7. So that is our answer choice. See you in the next video.

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Key Concepts

Mendelian Inheritance

Phenotypic Ratios

Segregation of Alleles