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:

Table showing summer squash crosses and fruit color ratios for genetics study.
Examine the results of each cross and predict how many genes are responsible for fruit-color determination in summer squash. Justify your answer.

Accepted Answer

Hi, everyone. Let's look at our 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 progeny resulted in 9/ plants with pink flowers and 7/16 plants with purple flowers determine the number of genes in which variable alleys segregate. And our answer choices are A one B two, C three N D four. Well, we have a really complicated question here. So let's kind of organize what we're given. We know we have P- 1 and P- 2. Both homozygous as their true breeding. We know they have different genotypes from each other as there are two different strains but both lead to purple flowers. So two different genotypes but same phenotype. And we know that when either of these is crossed with strain X, we end up with pink flowers. So there's some sort of factor in X that is interfering with the expression of that purple phenotype. We know that strain X also must be homozygous as it's true breeding. But we don't know what its phenotype is. Just that when it's crossed with either P- 1 or P2, we have this pink phenotype. Then when P one and P two are crossed with each other, we end up with pink flowers. And then when this F one, pink generation is crossed with itself, we get this 9-7 ratio of pink, two purple flowers. Well, it says determine the number of genes. Well, when we look at this F one crossed with F one and we have that 9 to ratio, these are 9/16 and 7 16th. And whenever we have that 16th, that's going to make us think of having two genes, which would result in that 16 square foot square. And we can recognize that 9-7 ratio as an example of a die hybrid cross with complementary gene interaction interaction up here, which makes sense with our observation that breeding with strain X interferes with the expression of the phenotype of P one and P two. So we're going to guess that we have choice B2 here. If I were to test I'd pick two and move on. If we want to kind of just understand this thoroughly. Uh For the sake of explaining this problem, let's look what our probable genotypes would be, we can imagine we have two genes A and B and if X is going to be homozygous and sort of override the effects of P one and P two, we could guess that X has a genotype of big, a big A big B, big B. And now we can imagine that having a dominant allele of each trait is what results in that pink flower color. Well, in that case, we can theorized that the genotype of P one would be little, a little A big B, big B must be homozygous. And then P two is big. A big, a little B, little B, also homozygous two different genotypes for those two different strains and both resulting in a purple phenotype. If our theory is that you need two or a dominant ally in each gene to make the pink pheno type, these each have a gene being homozygous recessive A or B giving that purple phenotype. But when they're cross with each other, the F one generation will be heterozygous. For both traits, they will be big, a little A big B, little B having one dominant alley of each gives them that pink phenotype. Then indeed, our F two generation is a die hybrid cross because F one will be heterozygous for both genes. So that leads us back to our answer choices. And yes, we have two genes creating this effect with complementary gene interaction, that esthetic interaction between that we see with strain X and then strains P one and P two. So choice P two is our answer here. See you in the next video.

Watch next