Imagine that you set up a three point mapping cross to...

Imagine that you set up a three-point mapping cross to determine the order of three X-linked genes. You have recessive mutations available for all three genes: yellow, white, and echinus. A heterozygous F1 Drosophila female is crossed to a hemizygous mutant male. The observed numbers and phenotypes of F2 are as follows: 4685 yellow, white, echinus 4759 wild type 80 yellow 70 white, echinus 193 yellow, white 207 echinus 3 yellow, echinus 3 white Based on this data, which of the above phenotypic classes represent the PARENTAL types? Each answer yields a clue useful in the following question. Choose all that apply.

Transcript

00:01 When we want to know about information about the genes of a generation where we want to know perhaps the order of the genes, which gene is in the middle, or the recombination frequency, or how far apart they are on a chromosome, then we always start by listing them in order from the most common to the least common.

00:20 So you see here, i've started by seeing that the most common phenotype, there's 4 ,759, who are wild type, and so have all dominant traits.

00:29 Next most common have all processive traits.

00:34 And then i just go down the list, listing them in order, like i said, from the most common to the least common.

00:41 And we do this for a couple of reasons.

00:44 One of them is that we can see which offspring are the non -recognitants and which ones are the recomminants.

00:51 Now, non -recommonants are those offspring who do not experience crossover events.

00:57 So these are the offspring who just got a chromosome from each parent, no crossover, no swapping of alleles.

01:07 This is just the parental types.

01:10 So we would expect that one of our parents would have all dominant traits, would have a dominant phenotype, and one parent would have a recessive phenotype, all recessive traits.

01:20 Then that means that the rest of these that don't happen as frequently are recombinants.

01:25 Now there's a couple different kinds of recombinants.

01:27 There's single crossover or double cross over...

Question

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