Gene R and gene T are genetically linked. Answer the following...

Question

Gene R and gene T are genetically linked. Answer the following questions concerning a dihybrid organism with the genotype Rt/rT:

If two crossover events occur between these two genes, what are the genotypes of the recombinant chromosomes?

Accepted Answer

Hello, everyone. Let's look at our next problem. It says in crossover studies on maze, the following percentage of genes X Y Z and W crossed over between X and W 15% between X and Z, 4% between gene Z and W, 11% Between genes between genes X&Y, and between genes Z&Y 10% respectively. Therefore, the correct sequence of genes X Y Z and W on the chromosome is and my answer choices reflect different orders of the four chromosomes or between the genes. Sorry choice A X Y Z W choice B W Z Y X, choice C Y X Z W and choice D X Z W Y. So we know that recombination frequency is proportional to the distance between genes. So we can use that frequency to determine how far apart different genes are. And a good place to start when trying to map their location on a chromosome is to see, do we have any groupings where um numbers add up or two, numbers add up to another one, giving us a clue that maybe that's a group of three where one is in the middle So that's a little bit of a, a confusing explanation. It'll help just to dive in and see an example of that. So I'm going to pull out my information from my question text just to put it all together and be able to look at it at once. So I know I have X N W 15%. I have X and Z 4%. I have Z&W 11%. Then I have X&y 6%. I have Z N Y 10%. Well, right away, looking at my numbers, I see that the number is 4% and 11% Add up to 15%. So that maybe gives me a hint of the order those three might be in. So I have, I'm going to draw a line where I have 15% as the total length. And I know that that's genes X and W 15% is their recombination frequency. So at either end of the line, on the left side, I'll write X and on the right side, I'll write W of the 15% line and then adding up to 15% is 4% and 11%. So that will represent the gene in the middle. And when I look at the letters that does make sense, I have the distance from X to Z being 4% and the distance from Z to W being 11%. So that means I can put Z Here in the middle, it's going to be closer to X because the distance is only 4%. So I'll put z here. So now I have X on the left and then Z With a distance between them of four And then Z to W is 11 and that corresponds To the total length between X&W of 15%. So now I have the order of XZW. So now let's look at the rest of my data. Well, I've got X Y being 6% Z Y being 10%. Well, if I combine that with knowing that XZ is 4%, I have four and 6% equaling 10%. Well, it doesn't really work. That's giving me. So I have 4% is XZ 6% is XY and 10% is Zy. Well, I might try and put, um, so Z Y equals 10%. So that's my largest space. So I'm gonna look at the Z here which is in the middle of X and W and see what could I put it? Would I put Y 10% away and put it over here? So it's just shy of W&C and W are 11% apart. I'll tentatively try and put Z just before w sorry, not Z, excuse me. Um I'll try and put Y just before w so then I would have Z Y being 10% Z W being 11% Well, does that work with my other information? So then let's go to X&Y must be 6% apart. Well, currently I have X as being on the other side of Z farther away from Y N W. So according to my already drawn diagram, if Y is right next to W, then X and Y would have to be 4% which is the distance from X to Z and then 10% which is the distance from Z to Y, Which would give a total distance of 14% between X&Y instead of what I know it to be is 6%. So that indicates I'm gonna take away the why I tentatively drew in there, That Y is on the other side of Z. So still 10% away, that's still the biggest distance, but it's on the other side, so farthest away from W and I don't have any data on the distance between Y and W. So nothing to contradict that or confirm it. So I'm just gonna extend my line on the left past X and I'm gonna draw Y on there and indicate that Z and Y Have a distance of 10%. Now, does that work with that Z X value of 4% or X Z? And I know the distance between X and Z is 4%. So that can still stand because X is to the left of Z as is Y. So now I have Z to X is 4% Z to Y is 10%. So what's the distance between X and Y That is 6%? So that makes that add up because I have Z X 4% plus X Y, 6% equals 10% between Z and Y. Putting them going right to left Z X Y and my other grouping went right to left X Z W. So all the numbers add up here and that gives me an order of why X Z W. So when I look over at my answer choices, choice C is Y X Z W as the correct sequence of those four genes. See you in the next video.

Gene R and gene T are genetically linked. Answer the following questions concerning a dihybrid organism with the genotype Rt/rT:

If two crossover events occur between these two genes, what are the genotypes of the recombinant chromosomes?

Key Concepts

Genetic Linkage

Crossover Events

Recombinant Genotypes

Watch next