Bc3 and def4 are two loci in yeast when abc3 def4 haploid...

BC3 and DEF4 are two loci in yeast. When ABC3 def4 haploid yeast were mated to abc3 DEF4 haploid yeast, the resulting diploid sporulated, and the tetrads analyzed, it was found that the number of nonparental ditype tetrads and the number of parental ditype tetrads were both about 25%, About 50% of the tetrads were tetratypes. Which is true? Group of answer choices ABC3 and DEF4 are each far from the centromere of the chromosome that is on. It is impossible to tell if they are on the same chromosome. ABC3 and DEF4 are unlinked, and either ABC3 or DEF4, or both, but not necessarily both, are far from the centromere of the chromosome they are on. ABC3 and DEF4 are unlinked, and both ABC3 and DEF4 are close to the centromere of the chromosome that they are on. ABC3 and DEF4 are unlinked, and both ABC3 and DEF4 are far from the centromere of the chromosome they are on.

Transcript

00:01 If we are told that there are two genes, say a and b, and we know that they are 20 map units apart.

00:07 Well, that information is really useful because 20 map units apart is the same thing as saying 20 % recombination.

00:17 So that means that of the offspring, 20 % are going to experience recombination of genes a and b.

00:24 So knowing that those two numbers are the same is very useful when we look at genetics in determining map distance and amount of offspring we expect to have each phenotype, etc.

00:37 But when we look at this, if we have two genes that we say are connected and they're only 20 map units apart, then we would expect something like this where we have two chromosomes and on each of the chromosomes, you have an a gene and a b gene.

00:56 They both reside on the same chromosomes.

00:59 And so what you would expect is that most of the offspring are non -recombinant types, meaning that you get this chromosome or you get this one.

01:09 You're either going to get the dominant a recessive b as i've drawn here, or you'll get recessive a dominant b, right? you're just going to get one of the chromosomes as is.

01:21 However, some of the offspring will be recombinant type.

01:26 In this particular example, we would say that 20 % are going to be the recombinant type.

01:30 And that means that there will be some crossover like this.

01:34 So we would either get both dominant or we would get both recessive.

01:41 But if they're on the same chromosome as this and we say that they are linked, then we would expect most of them to get a chromosome from their parents with no recombination that happens.

01:52 However, if we see information that makes us think there is independent assortment instead, so they are not linked, it might mean that when we try to calculate recombination frequency, recombination frequency comes to something like 50%...

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