Pigment in mouse fur is only produced when the C allele is present. Individuals of the cc genotype are white. If color is present, it may be determined by the A, a alleles. AA or Aa results in agouti color, while aa results in black coats. In three crosses between agouti females whose genotypes were unknown and males of the aacc genotype, the following phenotypic ratios were obtained:
(1) 8 agouti
(2) 9 agouti
(3) 4 agouti, 8 white 10 black, 5 black, 10 white

Question

Pigment in mouse fur is only produced when the C allele is present. Individuals of the cc genotype are white. If color is present, it may be determined by the A, a alleles. AA or Aa results in agouti color, while aa results in black coats. In three crosses between agouti females whose genotypes were unknown and males of the aacc genotype, the following phenotypic ratios were obtained:

(1) 8 agouti

(2) 9 agouti

(3) 4 agouti, 8 white 10 black, 5 black, 10 white

Accepted Answer

Hi everyone, welcome back. Let's look at our next question. It says the alley big Y. Which produces the yellow color of the seed in the p plant is completely dominant over little Y. Which makes the seed green. The alley for the round shape. Big R. Is completely dominant over the wrinkled shape. Little are what will be the fanatical ratio of a cross between Big R. Little R, big y. Little Y. And big R. Little R big y. Little Y. Well, that's your call. As we look at the cross they're asking us to look at and show its fanatic ratio. These parents have the same genotype and both of them are hetero sickness for both traits. And let's recall it. That's called a die hybrid cross. And this is kind of a useful one to know. Um it's kind of a common cross that you see in genetics problems. And in terms of getting through tests quickly, um it's kind of one that I'd recommend having memorized. So the fanatic ratio that you see of a dye hybrid cross is 9-3-3-1. And we're gonna go ahead and highlight that over here. That's choice B as our answer. And those ratios have a meaning of nine Of the offspring. When you draw your Punnett Square, showing 16 possibilities for offspring are going to be show the dominant trait. We're both traits and of course that's going to be the largest number since the phenotype will show the dominant trait. If it's either homogeneous dominant or hetero sagas, Then each of the three is here will be cases where the offspring is dominant in one trait and recessive in the other. And finally the one will be offspring that are recessive in both traits. So that will be our ratio for the offspring. And if you'd like to see the full planet square showing how we come up with this ratio, just keep on watching. I'll put that up. So let me just put up our grid for our 16 possibilities. And we're right in the parents, Jenna types. So both are the same. So we write the possible gametes from each of these parents. So we have the big are in combination with other big Y. Or little Y. And a little R. In combination with big Y. Or a little Y. And then obviously the same four combinations since the parents have the same genotype. Now you can see when you look at this square that if we want to talk about the offspring that will be recessive in both traits. So they have to inherit recessive values for both traits from both parents. That's only going to occur in this one square here. So I'm gonna go ahead and sort of color that in. Great to sort of show that we already identified that as recessive in both traits and now I'm gonna go ahead and fill in the rest of the squares with the different possibilities. I'm just going to paste it all in. So you don't have to watch me write that all out. And it's good to note as we look at our all our genotype combinations that it's often easier to look for the recessive traits as we started looking for the offspring with recessive in both traits. Um Since there's only one possible genotype for recessive trait obviously which is the homos I guess recessive. So we'll start with looking for something that's homocide is recessive for little are obviously we have our box already grayed out here for both recessive and we see that that possibility occurs here. We've got a little our ally little are alittle happening in this column here And then these two boxes here where little R. S. Inherited from both parents. But you see the dominant um yellow trait on the other as well. So there's our three dominant and one recessive than the other. Now we'll switch colors here and we'll look for things that are recessive for the wrinkled shape. Um but dominant for the yellow color. So now we're looking for a little y little y. And we see that again we have the great out square where we've got both recessive traits. So we see little y. Little Y over here in this column and then we see it occurring twice here in this column. So there's our three dominant in the other trait with recessive in the second. And finally we look at all our remaining squares over here and we can see that in every case. Each of them has at least one dominant allele in both traits. And we see that as we go down these columns, obviously because we've got um Big R. Big Y. Coming down here, Big R. Big Y. Coming across here, And then these remaining two. And that's going to give us our nine offspring showing dominant traits in both characteristics. So again, our phenotype phenotype ratio of that dye hybrid cross between Big R. Little R, big Y, little Y. And big R. Little R. Big Y. Little Y. Is 9 to 3 to 3 to 1, which is choice B. See you in the next problem.

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Key Concepts

Mendelian Inheritance and Allele Segregation

Epistasis and Gene Interaction

Genotypic and Phenotypic Ratios in Dihybrid Crosses