An interrupted mating study is carried out on Hfr strain...

Question

An interrupted mating study is carried out on Hfr strains 1, 2, and 3 identified in Problem 17. After conjugation is established, a small sample of the mixture is collected every minute for 20 minutes to determine the distance between genes on the chromosome. Results for each of the three Hfr strains are shown below. The total duration of conjugation (in minutes) is given for each transferred gene.

Hfr strain 1 oriT met ala lac gal
Duration (min) 0 2 8 13 17
Hfr strain 2 oriT met leu thr azi
Duration (min) 0 2 7 10 17
Hfr strain 3 oriT gal pro trp azi
Duration (min) 0 3 8 14 19

In minutes, what is the total length of the chromosome in the donor species?

Accepted Answer

Hello, everyone and welcome to today's video. So, an interrupted mating experiment is used to study the distance between genes on a chromosome. In this experiment, conjugation between an H F R strain and an F minus strain is interrupted at specific time intervals. And the resulting cells are plated on the selective media. The phenotype of the resulting colonies is used to determine the order and distance of the genes on the chromosome. So, and in an experiment involving three different H F R strings, the following data were obtained. So H F R strain one, the origin of transfer was transferred in zero minutes, gene A in two minutes, gene B in seven minutes and gene C in 10 minutes in the second strain. So in H F R strain two, the original transfer was transferred in two minutes, gene A in two minutes, gene C in eight minutes and GB in 12 minutes. For H F R strain three, the original transfer was transferred in zero minutes. Then gene C in three minutes, then gene A GB in eight minutes and gene A in 15 minutes. So what is the order of the genes on the chromosome? In the donor string. So we have as answer choice A AC, then B, then answer choice B, we have C B then A as answer choice C, we have B AC and as answer choice D we have ABC. Well, all we have to do in order to solve this problem really is look at these transfer times starting by the origin of transfer. So always your original transfer will be the first one or the first to be transferred starting at zero minutes. Then looking at these transfer times of gene A, we can see that gene A was transferred first in H F R strains one and two with a transfer time of two minutes. However, H F R strain three had gene C being transferred in three minutes. But because gene A is shorter than three, we're going, we're going to put gene A next with two minutes. Then we have GB as the second to be transferred in hr strain one gene C as the second to be transferring H F R strain two and gene B again as the second to be transferring H F R strain three. Now, because gene B was transferred at a shorter time than gene C in HFR strains one. And so here we have that gene B is going to be the second one that is going to be transferred with a transfer time of seven minutes. And then we have finally, gene C, which is the only one remaining with a transfer time of about 10 minutes. Now, because of this, the correct order here is going to be A then B then C which is going to be represented by answer choice D ABC. I really hope this video helped you and I hope to see you on the next one.

Key Concepts

Hfr Strains and Conjugation

Gene Mapping and Time of Transfer

Chromosome Length Calculation

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