A wheat variety with red kernels (genotype A^' A^' .B^' B^') was crossed with a variety with whi

A wheat variety with red kernels (genotype A^' A^' .B^' B^')...

A wheat variety with red kernels (genotype $A^{\prime} A^{\prime}$ $\left.B^{\prime} B^{\prime}\right)$ was crossed with a variety with white kernels (genotype $A A B B$ ). The $\mathrm{F}_{1}$ were intercrossed to produce an $\mathrm{F}_{2}$ If each primed allele increases the amount of pigment in the kernel by an equal amount, what phenotypes will be expected in the $\mathrm{F}_{2}$ ? Assuming that the $A$ and $B$ loci assort independently, what will the phenotypic frequencies be?

Key Concepts

Additive Gene Effects

This concept refers to the phenomenon where each allele contributes an equal and cumulative effect to the phenotype. When alleles act additively, having more copies of a specific allele results in a proportional increase (or decrease) in the trait value, leading to a range of phenotypes rather than discrete classes.

Independent Assortment

Independent assortment is the principle that alleles for different genes segregate independently of one another during gamete formation. This is crucial for predicting the phenotypic ratios in multi-gene crosses because it allows the calculation of combined probabilities for each genotype and, consequently, each phenotype.

Incomplete Dominance

In incomplete dominance, the heterozygote exhibits an intermediate phenotype between the two homozygous phenotypes. This occurs because neither allele is completely dominant, and the effect of each allele is only partially expressed, which is key to understanding how additive gene effects produce intermediate phenotypes.

Dihybrid Cross Analysis

Dihybrid crosses involve two genes, each with two alleles, and are used to examine how traits are inherited simultaneously. Through this analysis, especially under additive effects, one can predict the distribution of phenotypes in the offspring by summing the contributions from each gene, resulting in a range of phenotypic classes based on allele dosage.

Transcript

00:01 All right, so we're going to address the question that asks about crossing red kernels of wheat with white kernels of wheat.

00:08 The first part of this question asks about basically what phenotypes will be produced in the f2 generation.

00:20 And so the main things we have to really look out for in that first part of the question is that it states that if each prime allele increases the amount of pigment in the kernel by an equal amount, what phenotypes will be expected.

00:35 And so that means, for instance, if we are working with, let's say, this versus this for the genotypes, the top one here has one, two, three, four primed alleles.

00:58 Each of those is associated with the red pigment.

01:04 On the bottom here, there are zero primbileals.

01:10 And so that means this one on the bottom here, this plan or this kernel would be completely white, or the one on the top would be completely red.

01:19 And so it kind of also has to do with generations down the line too.

01:24 For instance, if we had one, let's say that was an example of one, that was further down one of the generations.

01:35 It only has one to three pomedolios, which means it's going to be some variation or somewhere on the scale between red and white closer to red.

01:50 And so again, this is a really important part of the first question here.

01:57 So make sure you really read over that before you go into detail about the second part of the question.

02:04 But let's kind of get into it.

02:06 Initially, it states that we have, again, the two kernel types, the red, which are right here on the top.

02:21 And then we have the white too.

02:27 And i'll just mark this as red so we know.

02:35 So it says that the red kernels were crossed with the white kernels to produce f1.

02:43 And so basically what that means is that these guys were both crossed to produce this.

02:56 Again, so note that on there we only have one, two primed alleles there.

03:09 And so that means that this plant would be kind of like a pinkish color because it's half red, half white.

03:18 So let's see.

03:19 Then it says the f1 generations were intercrossed, so bred with, basically bred with the same genealotype, to produce f2.

03:30 And so here is where we're going to draw a punnet square really quick, just to give you a quick example.

03:35 I'm not going to fill it in all the way, but i'll just kind of fill it in a little bit, and you guys can finish the rest if you'd like to.

03:43 And so going off again, or going off on that, just remember that this one's going to be f1, and then we're going to do the f2 because it was intercrossed.

03:58 And so let's draw that punnet square really quick.

04:01 So on the top here, again, we're going to have, again, it's going to have, again, it's going to going to be the same on the other side because again, they're intercrossed.

04:39 Cool.

04:40 So that's kind of the beginning of the point...

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