Question

You are performing an interrupted mating experiment testing for transfer of lac, gal, str^R, ile, trp, ton^R, and val. You have the following plates available to you:

Plate A: MM

Plate B: MM + lac + val + ile + trp

Plate C: MM + gal + T1 phage

Plate D: MM + val

Plate E: MM + streptomycin + ile + trp

Plate F: MM + lac + trp

Which of the above plates selects for transfer of the MOST genes?

a.

Plate A

b.

Plate B

c.

Plate C

d.

Plate D

e.

Plate E

f.

Plate F

g.

More than one of the above

Which of the above plates selects for transfer of the FEWEST number of genes?

a.

Plate A

b.

Plate B

c.

Plate C

d.

Plate D

e.

Plate E

f.

Plate F

g.

More than one of the above

To perform the interrupted mating experiment described above, which of the following Hfr strains would you use?

a.

Hfr lac+ gal+ strR ile+ trp+ tonR val+

b.

Hfr lac+ gal+ strS ile+ trp+ tonS val+

c.

Hfr lac+ gal+ strS ile+ trp+ tonR val+

d.

Hfr lac+ gal+ strR ile+ trp+ tonR val+ tetS

e.

Hfr lac+ gal+ strR ile+ trp+ tonR val+ tetR

Answer 1

In an interrupted mating experiment, the Hfr and F− cells are mixed, followed by conjugation and , the F− cells are sampled at fixed intervals to determine the transfer of donor alleles. The given experiment is to test for transfer of lac, gal, strR, ile, trp, tonR, and val.

So the Hfr with the highest number of genes will tranfer the maximum number of genes to the F- the lowest number of genes in Hfr will transfer the least.

Thus, the plate that selects for transfer of the MOST genes is b.Plate B

The plate that selects for transfer of the FEWEST number of genes is a.Plate A

Again, antibiotic sensitivity allele in the Hfr resistance allele in the F- are used to selectively kill the Hfr cells after conjugation by adding the perticular antibiotic to the mixture of cells after successful transfer. And Hfr must contain all the genes (denoted as +) that are to be transferred.  

So the strain used for the above experiment would be:

d.Hfr lac+ gal+ strR ile+ trp+ tonR val+ tetS

Tetramycin can be used to kill the Hfr and select the recombinants provided that the F- already had a tetR allele.

P.S. Please rate Thumbs Up if you liked it. Thanks.