2) (9 pts) We have an Hfr strain that is gal + met + arg + amp S and we wish to map the relative position of the met and arg genes.

2)   (9 pts)  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?

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