Question

A researcher is trying to assess whether or not two genes (G and Q) that determine coat color (brown-dominant or white-recessive) and hair length (short -dominant or long-recessive) in hamsters are linked. Describe the crosses they should perform to test for linkage and how the results from these crosses would answer their research question.

Answer 1

Answer:

Dihybrid testcross is used to know whether the two genes are linked or not.

If testcross ratio is 1:1:1:1, it indicates that the two genes are not linked and they are assorted independently.

Ex:

Brown, short (BBSS) x white, long (bbss)---Parents

BbSs (brown, short)----------------------------F1

BbSs (F1) x bbss (tester parent)—Testcross

	bs
BS	BbSs (brown, short)-25%
Bs	Bbss (brown, long)-25%
bS	bbSs (white, short)-25%
bs	bbss (white, long)-25%

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If testcross progeny do not fit into the 1:1:1:1 ratio and recombinant progeny are produced in less number than the non-recombinant progeny. It indicates that the two genes are linked.

Ex:

Brown, short (BBSS) x white, long (bbss)---Parents

BbSs (brown, short)----------------------------F1

BbSs (F1) x bbss (tester parent)—Testcross

	bs
BS	BbSs (brown, short)-more than 25% (non-recombinant)
Bs	Bbss (brown, long)-less than 25% (recombinant)
bS	bbSs (white, short)-less than 25% (recombinant)
bs	bbss (white, long)-more than 25% (non-recombinant)