You cross your newly isolated dominant mutation 410 to a...

You cross your newly isolated dominant mutation (410!!) to a "tester" strain with the two markers apple and banana. From the F1 (apple banana / 410!!), you isolate recombinants that show either the apple phenotype or the banana phenotype (are either apple banana+ or apple+ banana). Of the apple banana+ recombinant chromosomes, 99 of 100 are 410!! Of the apple+ banana recombinant chromosomes, 0 of 100 are 410!! Apple is to the left of banana on the genetic map. Where is 410!! most likely to map?

Transcript

00:01 We want to know information about the recombination of genes.

00:03 We always need to start in the same place, which is taking that list of eight different phenotypes in our f1 generation and listing them from the most common to the least common.

00:15 So starting with the type that has the most offspring, there's a couple that have 700 offspring for each phenotype.

00:26 So the top one is recessive a, dominant b recessive.

00:30 C.

00:32 Another one is dominant a, recessive b, dominant c.

00:37 All right.

00:37 And then we go to the next common one.

00:39 This one has 95 and it is all dominant a, b, c.

00:45 Next one also has 95 and it has all recessive.

00:49 And then we're just going to keep listing them in order from greatest to least.

00:55 And that does a couple different things for us.

01:00 So once we do that, we can identify the top two.

01:03 The ones that have the most common phenotypes are the parental types, meaning that these are the combinations you would get if there was no recombinations that happened during the formation of the gametes.

01:20 All of the others are some form of recombination.

01:23 It might be, you know, one or two alleles that are recombined.

01:28 However, the last two are important because when we compare the last two to the first two, so the last two, the ones that are the least common, to the parental types, we can tell which allele is in the middle.

01:42 The reason why is that these last two, you can see that they happen drastically less often than anything else.

01:49 They almost never happen.

01:52 That's because in those two, you see that only the middle allele gets recombined.

02:00 It's not often that you're going to combine the middle allele and not one of the two.

02:04 Next to it.

02:06 So it happens very rarely and thus it's easy to identify.

02:09 So how we do that is compare these bottom two to the parental types.

02:16 So for example, i can look at this top parental type and i see that there is recessive a, dominant b, recessive c.

02:24 I can compare it to one of these lower types and i see one that's similar where it's dominant a, dominant b, recessive c.

02:33 In that case if i compare them the thing that's different is the a.

02:38 And then the other parental type, dominant a, recessive b, dominant c.

02:43 I compare it to this bottom one, recessive a, dominant b, or sorry, recessive b, and then dominant c.

02:50 And again, the thing that's different is the a...

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