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Help! Third year Genetics Resit - epistasis watch

    • Thread Starter

    Found out my resit is a lot earlier than I thought and I am still having trouble with a few concepts of my genetics revision. Seeing as lecturers are on holiday and/or unwilling to help I thought someone here might..

    This is an example of the type of question I'm struggling to answer and appears frequently throughout my past papers.

    From a screen for C.elegans mutants that show a paralysed phenotype the e1500 mutation was identified. The mutation was found to affect the unc-93 gene.

    a) crossing unc-93(e1500) mutants with wild-type males gave only paralysed F1 cross-progeny. Approx. 75% of the F2 progeny of these animals were paralysed with the remainder showing wild-type movement.

    Draw a scheme to indicate the likely genotype of the parental, F1 and F2 generations, and explain what sort of mutation e1500 is likely to be (25%)

    b) You mutagenise unc-93(e1500) homozygotes to identify suppressor mutations, and identify two mutants - X1 & X2 - which show wild-type movement. IN BOTH CASES THE ORIGINAL MUTATION WAS FOUND STILL PRESENT. You cross X1 and X2 mutants with wild-type males.
    The F1 progeny derived from X1 are all wild-type, as are their F2 self-progeny.
    The F1 cross-progeny derived from X2 are all paralysed, but only 56% of the F2 self-progeny are paralysed.

    You develop an antibody to the protein product of the unc-93 gene. The following table shows the results of the western blotting using different samples derived from the different C.elegans mutants.

    Genotype Unc-93 detected
    Wild-type Yes
    Original unc-93(e1500) Yes
    X1 No
    X2 Yes

    explain these observations and use them to explain the likely basis by which the unc-93(e1500) mutation is suppressed in the X1 and X2 mutants (75%)

    I should mention that in part a) the part i don't get is 'cross-progeny'. The question doesnt state what the F1 were crossed with. I'd assume they were back crossed with the wild-type males? And if so wouldn't this make the mutation a recessive or dominant negative?

    Cheers for any help
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