Suppose a polygenic system for producing color in kernels of a gr...

Question

Suppose a polygenic system for producing color in kernels of a grain is controlled by three additive genes, G, M, and T. There are two alleles of each gene, G₁ and G₂, M₁, and M₂, and T₁ and T₂. The phenotypic effects of the three genotypes of the G gene are G₁G₁ = 6 units of color, G₁G₂ = 3 units of color, and G₂G₂ = 1 unit of color. The phenotypic effects for genes M and T are similar, giving the phenotype of a plant with the genotype G₁G₁M₁M₁T₁T₁ a total of 18 units of color and a plant with the genotype G₂G₂M₂M₂T₂T₂ a total of 3 units of color.

How many units of color are found in trihybrid plants?

Accepted Answer

Hi, everybody. Here's our next problem. It says a breed of rabbits has two genes that determine their fur color gene A has two allys A one and A two that produce brown and white fur respectively. While Gene B has two alleles B one and B two that produce black and gray fur respectively. A rabbit with genotype A one A two B one B two has a mix of brown, white, black and gray fur. While a rabbit with genotype A one A one B two B two has only brown and gray fur. What is the possible fur color of a rabbit with the genotype A two A two B one B two? And our choices are a brown and white fur, B, white and gray fur, C, brown and black fur or D white, black and gray fur. Well, let's look at the information provided by our problem to analyze how the alleles interact with each other. So we have two different genes, each with two alleles. Well, our first rabbit genotype that were provided a one A two B one B two shows the effect of having both genes and being heterozygous for both of them. And we see that there's a mix of all the colors. So all of these alleys are therefore expressed simultaneously with no masking, no interference, either between the two allies themselves or of the one gene on the other. So we see here a case of codominance in the case of both of our genes. So codominance is when you do see that mix of colors like a roan horse or cow. So the genes expressed at the same time, no masking at all. And that's confirmed their second example where the rabbit with genotype A one, A one B two B two has brown and gray fur expressing simultaneously the two genes in their homozygous state that it has. So being that lets us know that being homozygous doesn't have any effect. There are genes where being homozygous might have some sort of masking effect. But we've seen that it doesn't you still see that uh simultaneously simultaneous expression? So now it asks us about a rabbit with a genotype A two, A two. So Homozygous for A two and then heterozygous for BB one and B two. So we know that all A two gives us the color of white, ilb, one gives the color black and A lb two gives the color gray. So again, it's a very simple, straightforward case of expressing each color that is present in the genotype. So we would expect our rabbit to have choice d white, black and gray fur expressing each of the colors in its phenotype. See you in the next video.

Key Concepts

Polygenic Inheritance

Additive Gene Effects

Genotype to Phenotype Mapping

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