Posted by selly on Sunday, April 7, 2013 at 8:58am.
You have discovered a new species of yeast and you would like to determine the pathway that this organism uses to synthesize the amino acid tryptophan.
This yeast species can take up tryptophan, or synthesize it on its own if tryptophan is not present in the environment. Furthermore, this yeast species is able to grow as a haploid or a diploid. Finally, two haploid cells of opposite mating types can fuse to form a diploid, and you can do this in a laboratory setting to study diploids or haploids.
You begin by collecting a set of 10 trp mutants, cells that are no longer able to grow on minimal medium unless tryptophan has been added. You label them "A" through "J". At this point, it is not clear that every mutation is in a different gene. That is, some of your mutations may have hit the same gene.
To determine the number of different genes you have mutated in your mutant collection, you conduct a complementation test. For each mutant strain, you form diploids one by one with all the other strains. You then see if the diploids can grow in the absence of tryptophan. You put your results in the table below. The symbol "+" means that the diploid can grow without tryptophan and the symbol "-" means that the diploid cannot grow without tryptophan.
A - - + + + + + + + +
B - - + + + + + + + +
C + + - + - - + + + +
D + + + - + + - + + +
E + + - + - - + + + +
F + + - + - - + + + +
G + + + - + + - + + +
H + + + + + + + - + +
I + + + + + + + + - -
J + + + + + + + + - -
(a) Based on these data, how many different complementation groups (genes) have you found in your 10 mutants.
(b) Assign each of the 10 mutants into complementation groups. Express your answer as a series of letters separated by commas. For example, suppose you had the mutants P, Q, R, S, and T. Further suppose that P and Q were in one complementation group, R and T are in a second group, and S is in a third group. You would enter the answer "PQ,RT,S".
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