An Hfr strain with the genotype cys⁺ lue⁺ met⁺ strˢ is m...

Question

An Hfr strain with the genotype cys⁺ lue⁺ met⁺ strˢ is mated with an strain carrying the genotype cys⁻ lue⁻ met⁻ strᴿ. In an interrupted mating experiment, small samples of the conjugating bacteria are withdrawn every 3 minutes for 30 minutes. The withdrawn cells are shaken vigorously to stop conjugation and then placed on three different selection media, composed as follows:

Medium 1: Minimal medium plus leucine, methionine, and streptomycin
Medium 2: Minimal medium plus cysteine, methionine, and streptomycin
Medium 3: Minimal medium plus cysteine, leucine, and streptomycin

What donor gene is the selected marker in each medium?

Accepted Answer

Welcome back, everyone. Here's our next question. The F plasmid contains two main loci and two other regions that help prevent the transferring of the F plasmid to an F plus cell. These loi include T R A and T R B locus. And the other two regions are the origin of replication or E V and the origin of transfer or E T, which region or locus codes for proteins that form the pie. So we're talking about the process of conjugation where we have an F plus cell containing a plasmid with the F factor or fertility factor. And F for joins with a pill eye structure two and F minus cell that doesn't contain a plasmid. And that plasmid gets replicated and transferred through the pill I to the F minus cell. You've got a donor and a recipient cell. So we're asked about the genes on the F plasmid which is very tiny, there's not much there. And it's saying which region or locus codes for the proteins that form the pie. And this is the T R A locus which is choice A, it contains the genes that help attach donor and recipient cell. And form the pill eye. Let's look at our other answer. Choices. The T R B locus codes for other proteins that help create the channel that goes through the pill I that joins the two cells. So that's not a correct answer. And then to IC or E T, the origin of transfer, this is where the enzyme relaxes N the plasmid so that it will become linear and be able to transfer through the pie but not what we're looking for. And then finally, choice D or E V is the origin of replication where replicate DNA replication of the plasmid starts, but that's not what we're looking for. Choice D is not correct. Again, the location that codes for the proteins that form the pill I that connects the two cells is choice A, the T R A locus. See you in the next video.

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