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SNP linkage

You are trying to map a human gene thought to be involved in cat allergies. Because
you know this gene is on chromosome 20, you decide to examine the linkage of
several SNPs located on chromosome 20 with respect to the gene involved in cat
allergies. You have obtained DNA from 10 individuals and know whether they
are allergic to cats. Your SNP results are shown in the table below.
SNP tests for chromosome 20. (+ = presence of SNP)
allergic to
cats?
SNP1 SNP2 SNP3 SNP4 SNP5
yes - + + + -
no - + - - +
no - - - - +
yes + + + - -
yes + - + + +
yes - - + + -
no + + - - +
yes + + + + -
yes - - + + +
no + - - - -
A. Which SNP is most likely to be tightly linked to the gene involved in cat
allergies? Explain your answer.

B. Of the SNPs tested above, which is likely to be the next closest to the gene
responsible for the allergic state? Why?

Solution Preview

In order to answer these questions, we need to determine whether any of the SNPs are ALWAYS associated with allergies.

Let's take a look at the data:

SNP1 SNP2 SNP3 SNP4 SNP5
yes - + + + -
no - + - - +
no - - - - +
yes + + + - -
yes + - + + +
yes - - + + -
no + + - - ...

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