Three strains of green-seeded lentil plants appear to ha...

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.

If strains G₂ and G₃ are crossed, what will be the phenotype of the F₁?

Table showing F1 and F2 phenotypes of green-seeded lentil strains G1, G2, G3 crossed with yellow strain Y.
If strains G₂ and G₃ are crossed, what will be the phenotype of the F₁?

Accepted Answer

Hello, everyone and welcome to today's video. So, a cross was done between two true breeding genotypes, fully homozygous dominant for AM B and fully homozygous recessive for AM B. Now the F one progeny, those was so fertilized, it was crossed with itself. The F two progeny has a phenotypic ratio of 13 to 3. So which of the following statements about this cross is going to be correct as answer choice. A, we have genes A and B have the same basic effect as answer choice B. We have a dominant allele of either gene GEO is the same phenotype as answer choice C. We have gene A blocks the expression of gene B and as answer choice D, we have either gene alone produces a partial phenotypic effect. Now remember that here in the parent generation, in our P one generation, we're going to be crossing a fully homozygous dominant organism with a fully homozygous recessive organism that is going to yield in these F one generation, fully heterozygous organisms. As we can see that we just wrote down here, then we're told that they were self fertilized. So they were crossed with another fully heterozygous organism for genes A and B and that is what we're going to be writing down here. Now, we are told that in the F two progeny, there was a 13 to three phenotypic ratio for this progeny, which is not going to be the correct phenotypic ratio for this heterozygous cross that we have here. Now, why is this? Well, there must be some type of A P stasis going on. There must be some underlying gene interaction that is causing this phenotypic ratio. And as it turns out that gene interaction that has a 13- phenotypic ratio is called dominant suppression in which one gene is going to block the expression of another gene. In this case, it is gene A blocking the expression of GB. And if we look at the answer choices, answer choice C gene A blocks the expression of GB is going to be the correct answer to this question. I really hope this video helped you and I hope to see you on the next one.

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