PART B – Genetic mapping 1. For the mice above you also...

PART B – Genetic mapping 1. For the mice above you also wish to map the genes in questions, together with one additional character: ear size – Large ears (E) dominant over Small ears (e). Assuming these genes are all found on the same chromosome, we wish to find the relative location for these genes. We crossed a line of mice heterozygote to the three genes (pelage color, tail length and ear size), with recessive true breeding line (BbTtEe X bbttee), and got the following results. Black pelage, Long tail, Large ears 514 mice Black pelage, Long tail, Small ears 56 mice Black pelage, Short tail, Large ears 2 mice Black pelage, Short tail, Small ears 46 mice White pelage, Long tail, Large ears 37 mice White pelage, Long tail, Small ears 3 mice White pelage, Short tail, Large ears 67 mice White pelage, Short tail, Small ears 491 mice Use these data to calculate the map distances between genes. Also, draw a chromosome model, showing the map distance between the different genes. 10 points.

Transcript

00:02 So in order to determine the map distance between these genes, we're going to start by listing the different phenotypes of this generation in order from the most common to the least.

00:14 And there's a couple reasons why we do this.

00:17 So the first thing that we're going to utilize this for is to determine non -recommonant types, your two most common, and then the recommant types, all of your other phenotypes.

00:28 This is useful because if we look at the recommants, there's two that i'm.

00:32 Are far less common than all the others.

00:35 These are your double crossover events.

00:38 So your double crossover events, what happens there is we have a middle gene that stays put.

00:43 And then the gene to either side will exchange alleles with the sister chromatids, leaving your middle gene surrounded by new alleles.

00:52 And so now it seems out of place.

00:54 And if we compare this to our non -recommonant types, we can tell which gene is in the middle.

01:00 So i'm going to start by picking a non -recognite type here dominant dominant dominant comparing it to the most similar double crossover dominant recessive dominant and there's one that's different seems out of place that's probably our middle gene but we'll compare the other two just to be sure whether non -recomit recessive recessive other double crossover recessive dominant recessive so again t is the one that's out of place it's our middle gene we do this because when we look for map distance we really want to look for the distance between the middle and the other genes because that's the laziest way to do it and we always want to do a little bit less work.

01:41 So we're going to be looking for the distance between b and t and e and t, right? so from one side to the middle, from the other side to the middle.

01:51 And the way that we're going to do this is by finding the recombination percentage for those genes.

02:01 Because if i told you that 20 % of the offspring experience recombination of b and t, that means that b and t are 20 map units apart.

02:11 So to do this, we have to start by looking at what does it look like for b and t to be recombined? so to answer this, you see, i've rewritten my non -recombinate types, the original chromosomes.

02:21 I'm going to draw a circle from the t of one chromosome to the b of the other and vice versa...

Question

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