Complementation test

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Complementation test

Post by georgina_009 on Mon May 05, 2008 10:32 am

I have a qn that says:

5 mutant strains of fungus which couldn't synthesise amino acid arginine were isolated. Each has a single mutation. Complementation tests using the 5 strains were carried out and the results show below (+ means complementation and - means no growth) Table - http://i30.tinypic.com/mll06o.jpg

then it asks - what is the min. no. of diff genes involved in the biosynthesis of argenine?
Show which strains have mutations in which genes.

SO: does this mean two is the min no.? For the second qn I am not sure what that means. Im just a bit confused, any help would be appriciated
Thanks

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Re: Complementation test

Post by Alla on Tue May 06, 2008 5:44 am

Complementation test is very simple. If the progeny of the cross between two true breeding parents with the same phenotype has WT phenotype (gets rescued) then there are two genes responsible for phenotype.

So, in your case, you have 5 mutants but only 4 of those produce rescued WT phenotype with all other strains. The 2 strains that do not produce WT offspring (#3 &#4) when crossed to each other have mutation in the same gene. Thus, you have at least 4 different genes involved.

Without any further information I would have to assume that question "Show which strains have mutations in which genes" refers to which genes are the same and which are different from each other.

Good luck!

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Re: Complementation test

Post by georgina_009 on Wed May 07, 2008 5:37 am

Thanks for your help!
I'm pretty sure I've got it now
4 different genes and gene a - 1, gene b - 2, gene c -3 4, gene d - 5
Thanks again

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Part B

Post by georgina_009 on Wed May 07, 2008 6:28 am

I just ahve another qn about the second part of this problem
it says:
Each of the strains used above was tested on a medium that contained intermediates in the pathway for the synthesis of argenine. Results: (sorry I cant get a proper table but imagine it spaced out)


Mutant Intermediates
(in order) Nothing added, Glutamic semialdehyde, ornithine, citrulline, arginine
1 - + + + +
2 - - + + +
3 - - - + +
4 - - - + +
5 - - - - +

Then I have to draw a metabolic pathway for the synthesis of argenine and it should look like this
..................1............................2..............3...............4
precursor ----> intermediate A----> int. B----> int. C-----> final product

I have to identify the the step (1 2 3 4) that is affected by the mutation in each mutant strain.

My guess is pre - nothing, A-Glut, B-Ornth, C -cit, final - Arg
But I'm not sure how to figure out 1 2 3 4. Could you possibly tell me how to go about doing this qn?
Thanks

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Re: Complementation test

Post by Alla on Thu May 08, 2008 2:46 am

Your pathway is in correct order. Now, the 1st mutant was able to produce arginine as soon a Glut was added. That means that mutation is in the step prior to it: 1st step (Precursor --> intermediate) in the pathway is affected.

If you examine all you will find that whatever intermediate introduced into the media is the first to produce arginine, the mutant gene is responsible for the immediately preceding step in the process.

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Re: Complementation test

Post by georgina_009 on Thu May 08, 2008 7:21 am

Ok thanks
so would you say step one is affected by mutant one, step two by mutant two etc.?

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Re: Complementation test

Post by Alla on Thu May 08, 2008 11:38 pm

Correct!

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