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 - - + + + + + + + +
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.
unanswered
(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".
To determine the number of different genes mutated in your mutant collection, you need to analyze the complementation test results. The complementation test allows you to determine if two mutations are in the same gene or in different genes based on the ability of diploids to grow in the absence of tryptophan.
(a) To determine the number of different complementation groups (genes), you need to identify mutations that fail to complement each other, meaning that their diploids do not grow without tryptophan. If two mutants fail to complement each other, it suggests that they have mutations in the same gene, while if they complement each other, it suggests that they have mutations in different genes.
By analyzing the table above, you can see that there are four groups of mutants that do not complement each other:
1. A, B
2. C, E, F
3. D, G
4. H, I, J
Therefore, there are four different genes (complementation groups) mutated among your 10 mutants.
(b) Now, let's assign each of the 10 mutants into complementation groups based on the results:
Mutants assigned to complementation group 1: A, B
Mutants assigned to complementation group 2: C, E, F
Mutants assigned to complementation group 3: D, G
Mutants assigned to complementation group 4: H, I, J
So, the assignment of mutants into complementation groups is as follows:
Group 1: A, B
Group 2: C, E, F
Group 3: D, G
Group 4: H, I, J