Fly Crossing

Chris Jones jonesc at
Mon May 6 13:38:35 EST 1996

In article <318A7422.37B1 at>, John Chan <johnchan at> wrote:

> I'm I student from Montreal and our biology class is experiencing fly 
> crossing. My team crossed Wild males and dumpy sepia females(PxP). Then 
> we crossed the offsprings and we obtained these results: 268 Wild Wild, 
> 64 Wild Sepia, 76 Dumpy Wild and 17 Dumpy Sepia. The Chi-Square Test 
> rejected our results (Our hypothesis for the ratio is 9:3:3:1). 
> Considering the fact that there was no experiment or identifying errors, 
> how can I explain the rejection of the results by the Chi-Square Test.

John --

If you assume a 9:3:3:1 ratio is correct, what sorts of numbers would you
expect? If you anchor your estimate to the wild-type count of 268, then
you'd expect about 90 sepia, 90 dumpy, and 30 sepia,dumpy flies. You only
observed 70-85% of the sepia and dumpy flies you expected, and only about
50% of the double mutants expected. Does this suggest anything?

Chris Jones (jonesc at

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