The ku80 and p53 genes both
encode proteins that are involved in repair of DNA damage in human cells.
Mutations to these genes have been associated with some human cancers. You
would like to determine if the Ku80 and p53 proteins functionally interact with
one another and have decided to use Drosophila, which has homologous of
both these genes, as a model system to address your question. The Drosophila
Ku80 gene is on chromosome 2. There is a mutant allele of the Ku80 gene
available which is recessively lethal. It is maintained in a balanced stock
over an SM6, Cy balancer chromosome. You have males and females of this
balanced stock available to you. The p53 gene is on chromosome 3. There is a
viable mutant allele of p53 available in a homozygous stock which is also
homozygous for a recessive mutation (e) at the ebony body locus which is also
on chromosome 3. You have both males and females of this double mutant stock.
In addition to the two stocks mentioned here, you also have access to both
males and females of the double balancer stock from question 1. In order to
test for potential functional interaction between the Ku80 and p53 proteins, Yu
need to generate a stock that contains both these mutations.
Your goal is to clearly outline
a series of crosses that will allow you to generate a new stock that is
heterozygous for the ku80 mutant allele over the SM6, Cy balancer and
homozygous for p53 and e. In other words, your desired stock of males and
females will have the genotype: ; ku80/SM6, Cy ; p53, e/p53, e. For each cross
you carry out CLEARLY indicate the genotype of each parent, and the genotype
and phenotype of any selected progeny you wish to continue to work with. You
only need to show the genotype and phenotype of your selected progeny (not
every possible progeny class). Hint: You will require multiple crosses to
achieve your goal. Some can be done in parallel (i.e. not dependent on each
other) while others will be dependent on progeny from a previous cross.
Remember that male Drosophila do not have recombination (no
crossing-over). Also keep in mind that if you are going to select a particular
progeny class for further work, they must be phenotypically distinct from all
other progeny classes or you would never be able to actually select them! (15
marks).
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