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ID 16420

Problem 18: Bacteria and viruses have DNA too.

Description:
Understand bacterial conjugation.
Transcript:
HI! In bacterial conjugation, the transfer of genes is directional, from a donor to a recipient. The donor "male" has a fertility factor (F+) that is itself heritable. Recipient females do not have the F factor and are F-. Bacteria that have the F factor make the pili needed for conjugation. This F factor is a piece of DNA that can exist on its own in the cytoplasm. This DNA can also be integrated into the bacterial genome through recombination. This F factor is a piece of DNA that can exist on its own in the cytoplasm. This DNA can also be integrated into the bacterial genome through recombination. What do you think happens if the F factor is integrated into the genome of a bacterium? The bacterium becomes F-, and can only act as the recipient. (No, the bacterium still has the F factor, so it cannot be the recipient.) The bacterium is F+, and is the donor. (That is correct.) The bacterium is F+, but can no longer be a donor. (No, the F factor is present, so the bacterium can make pili and be a donor.) The bacterium is F+, but is now the recipient. (No, a bacterium with the F factor is not a recipient.) When the F factor is integrated into the bacterial chromosome, it can still act as the donor in a conjugation cross. These integrated strains are called Hfr, because of the high frequency of recombination that occurs when mated with F- bacteria. In 1957, these Hfr strains were used to map the bacterial chromosome. You are going to do a mapping experiment using two bacterial strains. The Hfr strain is met+ bio+ thr+ pro+. The F- is met- bio- thr- pro- str+. The F- strain is resistant to the antibiotic, streptomycin (str+). You grow the bacteria together. Every five minutes you take a sample and shake it up in a blender to disrupt mating. You then plate the bacteria to test for recombinants. What kind of plates will you use to test these samples? complete media (No, all types of bacteria will grow on complete media plates.) complete media with streptomycin (No, you are only selecting for bacteria that are streptomycin resistant.) minimal media with streptomycin (No, you are only selecting for bacteria that are streptomycin resistant and have all the genes.) minimal media plates with three of the four supplements (No, you'll get Hfr bacteria growing on the plates as well as any recombinants.) minimal media plates with streptomycin and three of the four supplements (That is correct.) You want to plate the samples on minimal media with streptomycin to kill parental Hfr bacteria. You also want plates that will select for the specific markers that have been transferred. So, you'll use minimal media plates that have three of the four supplements. STR MET BIO THR (missing PRO) STR MET BIO PRO (missing THR) STR BIO THR PRO (missing MET) STR MET THR PRO (missing BIO) Based on this information, what is the order of transfer of these genes during conjugation? Choices: bio met pro thr (No, bio is not the first gene transferred.) thr pro bio (No, you're missing a gene.) thr pro bio met (That is correct.) there is no order. (No, there is an order to the gene transfer.) In your Hfr conjugation experiment, the order of the gene transfer is thr pro bio met. If we represent the bacterial DNA as a closed circle, then we can map the genes based on the order and time of transfer. When you compare results, his gene order is different from yours. What does this mean?
Keywords:
bacterial conjugation, antibiotic streptomycin, bacterial chromosome, bacterial genome, recombination, blender
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