Five Hfr strains from the same bacterial species are analyzed for their ability to transfer genes to F⁻ recipient bacteria. The data shown below list the origin of transfer (oriT) for each strain and give the order of genes, with the first gene on the left and the last gene on the right. Use the data to construct a circular map of the bacterium.
Hfr Strain Genes Transferred
Hfr 1 oriT met ala lac gal
Hfr 2 oriT met leu thr azi
Hfr 3 oriT gal pro trp azi
Hfr 4 oriT leu met ala lac
Hfr 5 oriT trp azi thr leu met

Question

Five Hfr strains from the same bacterial species are analyzed for their ability to transfer genes to F⁻ recipient bacteria. The data shown below list the origin of transfer (oriT) for each strain and give the order of genes, with the first gene on the left and the last gene on the right. Use the data to construct a circular map of the bacterium.
Hfr Strain     Genes Transferred
Hfr 1         oriT met ala lac gal
Hfr 2         oriT met leu thr azi
Hfr 3         oriT gal pro trp azi
Hfr 4         oriT leu met ala lac
Hfr 5         oriT trp azi thr leu met

Hfr Strain Genes Transferred

Hfr 1 oriT met ala lac gal

Hfr 2 oriT met leu thr azi

Hfr 3 oriT gal pro trp azi

Hfr 4 oriT leu met ala lac

Hfr 5 oriT trp azi thr leu met

Accepted Answer

Hi, everyone. Here's our next problem. Interrupted mating experiments can be used to determine the order of markers entering a recipient cell for any H F R strain. What is the order of markers in the F plus strain? If the following data is obtained from several H F R strains derived from the same F plus, we have a list of our H F R strains with markers that have transferred over H F R strain. One is R H E Z with a little arrow pointing to the right H F R stream, two K OS Z with a little arrow to the right H F R stream, three O K W I arrow to the right H F R stream four RT I W arrow to the right N H of R stream five H RT I. And our answer choices for the correct order of markers in the flu strain are choice A R H E Z O K W I T s choice B K OS R E H Z T I W choice to see R H E Z S O K W I T or choice D, none of these. So we have to be aware of that, it could be that none of these are correct. So we know that the markers that are transferring over are on a circular plasmid. So I start by drawing a circle to remind myself that again, we can start and stop in different places and we're going around in a circle, it's not linear. So we could have overlap happening in different directions based on our strands. So now we'll start writing in our different strands and seeing where they overlap to get the total overall order of those markers. So let's look at strain one and I'll just write these on the circle and it's starting anywhere. So I have R H E Z. So now let's look for at our next stream. Is there any overlap? Well, that gives me K OS Z? Well, I've got Z in common, but I know from my strain one that E is on one side of Z. So these must be the letters on the other side of that Z. So that must, this must go backwards to the order listed. So from Z will go next to S and then O and then K. So we've got a long strand here with the Z as our common letter. So let's move on to strain three and see if those overlap. Strain three says O K W I, well, here our overlap is the letters O and K. So I'll look down where I have O and K already on my circle. So I'll continue. I've got O K and then W I on my circle. Now, let's look at Strain four RT I w well, I just listed W and I, I've got them in the other order here are, and are I and W and then I've got R, well, R if you recall was the very first letter I put on my circle. So this gives me RT I W so I must have T on my circle between R and I. So I've put T to the left of R in my circle and that when I read it in that direction, RT I W so I now have presumably all my letters since I've overlapped completely. But we can double check with our last strain five H RT I. And indeed, there we have that overlap between the first strain we looked at R H E Z and then the last little bit we just put on RT I W. So H RT I does confirm that order that we have. So now we have our letters in order around the circle. So let's compare it to our answer choices. So we'll start with choice A which begins with R. So we'll start here with I. And then the next letter is H E Z. That's all correct. So far, then it has O K but we filled in after Z S O K. So choice A is not correct. It doesn't correspond with what we've calculated. Then choice B starts with letter K. So we'll go to K on here and then it has K O. So we're going to the right as we've drawn on our circle here, K OS R but there we have S Z, not S R. So we've eliminated choice B. So let's go on to choice C choice C has starts with R. So we'll go up to our letter R here. It has R H E Z S O K W I T that corresponds exactly with what we've written. So choice C must be our answer. We can go ahead and eliminate choice D, none of these since we have a correct answer. So our interrupted made an experiment to show us the order of markers in our F plus stream with the data we're given for our five H F R strains shows us that the order of markers is choice C R H E Z S O K W I T see you in the next video.

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Key Concepts

Hfr Strains and Gene Transfer

Gene Mapping

Circular Chromosome Structure in Bacteria