We have an Hfr strain that is gal+ met+ arg+ ampS and we wish to map the relativ

Question

We have an Hfr strain that is gal+ met+ arg+ ampS and we wish to map the relative position of the met and arg genes. We cross this strain with an F- strain having the genotype gal- met- arg- ampR. We know from an interrupted mating experiment that gal enters last. Note that gal = a carbon source (galactose) while arg and met are amino acids. Amp = an antibiotic.
If you plate on the following media:
Media A) minimal media lacking arginine but containing methionine
Media B) minimal media lacking methionine but containing arginine
Media C) minimal media lacking arginine and methionine
Media D) minimal media containing arginine and methionine

You obtain the following results:
Result 1) 5% of the recombinants are arg- met-
Result 2) 10% of the recombinants are arg+ met-
Result 3) 0% of the recombinants are arg- met+
Result 4) 85% of the recombinants are arg+ met+

Match the media with the correct phenotype.
What other chemical was in all the media? (why?)

Which gene is first?

How would you check to see if the galactose gene has moved?

Explanation / Answer

Matching the Media with correct phenotype:

Media A to Result 2

Media B to Result 3

Media C to Result 4

Media D to Result 1

Ampicillin wouid be added to all the media to enable the selection of recombinents, ie only those bacteria with recombinant gene would carry amp R gene and only those can survive in this media.

Since gal enters last, the order of gene should be arg, met,ampr gal, so the first gene should be Arg.

Growing the bacterial culture in a medium containing galactose as the sole carbon source can enable us to check if gal has moved or not. Only gal containing bacterium can survive in this medium.

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