1. Zim aliens are highly social and love to talk with each...

1. Zim aliens are highly social and love to talk with each other. However certain Zims can only hear communication at low frequencies. Others can only hear at high frequencies. Upon a visit to the planet, a geneticist did a phenotype count of 1000 Zims. She found 592 Zims that heard only low frequency and 418 that only heard at high frequency. However, she noted that all of the high frequency Zims lived in the mountains while the low frequency ones lived in the valley. Make a hypothesis about the mode of inheritance and then describe what is happening at a molecular level.

Transcript

00:03 So for this question, we're going to be looking at three different genes, q, b, and s.

00:08 We are told that q and b are 15 map units apart, s and b are 20 map units apart.

00:15 And then we know the genotypes of the two parents involved.

00:20 We know that one parent has all dominant alleles on one chromosome and all recessive on the other.

00:30 Whereas the other parent has only recessive alleles on both of their chromosomes.

00:36 So we're basically doing a test cross where one parent is heterozygous and one parent is completely recessive and so can be our test cross, meaning that they don't determine the phenotype of the offspring.

00:50 What's going to determine phenotype is whether or not we get any of these dominant alleles from the first parent.

00:56 So that's really what we're going to focus in on, which makes all of the mass a lot easier.

01:00 So the way that we're going to figure out what we should expect for all of the offspring of this couple is by calculating all of the possible events, double crossovers, single crossovers, and non -recombinate types.

01:13 We always start with double crossovers.

01:15 The way that we calculate this is we take the frequency of recombination between the genes.

01:22 So the frequency of recombination between b and q, since they are 15 map units apart, frequency of recombination is 0 .15.

01:32 We're going to multiply that by the frequency recombination of b and s.

01:35 Since they're 20 map units apart, it's 0 .2.

01:39 And then you would multiply that by the number of offspring that you would expect from the couple.

01:48 Now since we are not told how many offspring they're going to have, what i'm going to do is just multiply it by 100%.

01:54 That way all my answers are in percentages and it makes it really easy to read if you ever are given that information labor.

02:02 So we're just going to go ahead and do that math.

02:04 0 .15 times 0 .20 times 100%.

02:07 You end up with 3%.

02:10 So i would expect 3 % of my offspring to be double crossovers.

02:17 And then i'm going to go down.

02:17 I'm going to do the same kind of thing for a single crossover event.

02:21 Now, there's two kinds of single crossover events we can happen.

02:24 We can have a single crossover event of q and b, or a single crossover event of b and s.

02:31 So we're going to have to calculate each of those individually.

02:35 So for qmb, what we do is take the frequency of q &b, so which we found to be 0 .15, and then multiply it by that 100%, and then subtract your double crossover...

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