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Calculating the cross over value using a test cross
I. Drosophila: Studying the wing shape and body colour
These results are, therefore, typical of non-linked genes. The recombinants are in the same frequency as the parental combinations. Note: In this example bent wing flies are a bit crippled so their offspring are not so viable. This accounts for their low numbers.
II. Drosophila: Studying the eye colour and body colour
The frequency of the recombinants is less than 50% this is an example of linkage.
The % recombination in a test cross is called the cross over value.
The cross over value between ebony and pink =
This value is important as it tells us how far apart the loci of the genes are. Cross over values from several pairs of genes will permit a geneticist to plot a gene map of the chromosome.
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