Hfr strains that differ in integrated F factor orientation and site of integration are used to construct consolidated bacterial chromosome maps. The data below show the order of gene transfer for five strains.
Hfr Strain Order of Gene Transfer (First → Last)
Hfr A oriT–thr–leu–azi–ton–pro–lac–ade
Hfr B oriT–mtl–xyl–mal–str–his
Hfr C oriT–ile–met–thi–thr–leu–azi–ton
Hfr D oriT–his–trp–gal–ade–lac–pro–ton
Hfr E oriT–thi–met–ile–mtl–xyl–mal–str
Identify the overlaps between Hfr strains. Identify the orientations of integrated F factors relative to one another.

Question

Hfr strains that differ in integrated F factor orientation and site of integration are used to construct consolidated bacterial chromosome maps. The data below show the order of gene transfer for five strains.

Hfr Strain Order of Gene Transfer (First → Last)

Hfr A oriT–thr–leu–azi–ton–pro–lac–ade

Hfr B oriT–mtl–xyl–mal–str–his

Hfr C oriT–ile–met–thi–thr–leu–azi–ton

Hfr D oriT–his–trp–gal–ade–lac–pro–ton

Hfr E oriT–thi–met–ile–mtl–xyl–mal–str

Identify the overlaps between Hfr strains. Identify the orientations of integrated F factors relative to one another.

Accepted Answer

Hi, everyone. Welcome back. Let's look at our next question. It says E coli is used in an experiment to determine the order of genes. A cross was made between H F R H of genotype lac plus pro C plus gal plus and an F minus strain negative for all of these genes. After about two hours, the mixture was diluted and plated it out on a medium containing galactose as the sole carbon source and got the pattern gal plus 100% lac plus 30% pro C plus 45% determine the order of the genes. And our answer choices are a lax pro C G. Choice B pro C lack gal choice C G lack pro C and choice D G pro C lack. So we know that we need to look at how many of the different colonies that grow have the different genes as expected. Since our medium has galactose as the sole carbon source, we have 100% of the colonies that grow being Galp plus because they won't grow if they don't have that gene. Now, if another gene was closer to that origin of transfer than gal, you would expect to see that gene being positive in 100% of the colonies as well. Uh Because anything that got transferred over containing, say a lac gene, but not a gal gene would not grow on this medium since it doesn't have the gene to use galactose. But since our other two genes lack and pro C are positive in less than 100% of our colonies that grow, we know that they must have transferred after the gal gene. So our gal gene must be first. So we can eliminate answer choices that don't have it as the first gene. So choice A has lack first. We cross that out and choice B has PRO C first so we can eliminate those answer choices. So we know we have gal first and they will want to look at the percent of colonies having the other genes knowing that again because they transfer in order, you'd expect to see a greater percent positive for the gene that comes next. Pro C is positive in 45% of the colonies while lack is positive in just 30% of the colonies. So we'd expect our order to be Gal pro C and then lack based on how many colonies have these genes present. So as we look at our answer choices, we see the choice of D is gal pro C lack. So that will be our answer while choice C has lack first before pro C So we'll eliminate that. So again, with these percents gal plus 100% lack plus 30% Pro C 45% the order of the genes is choice D gal pro C lack. See you in the next video.

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Key Concepts

Hfr Strains

Gene Transfer Order

F Factor Orientation