Genetic Study of the Yellow Body Mutation in a Small Community of Drosophila

Hypothesis
The parental Drosophila had genes of XyY and XX, with Xy being recessive to X. The genes expressed complete dominance and the trait is sex linked.
The null hypothesis: A 1 female WT:1 male WT ratio will be observed from the parental cross.


Procedure
I crossed two Drosophila Melanogaster, a yellow bodied male and a wilt type female. I then crossed the F1 generation to get the F2 generation.

Quick Results
I discovered that the y gene resides on the X chromosome and is recessive to the X chromosome.
Categories# Observed# Expected(o-e)2/e
Female WT
Male WT		24
25		25
25		.04
0.0

Σ(o-e)2/2 =0.0 + .04 =.04
Degrees of freedom=# of categories -1= 2-1= 1

When X2 =.04 and there is 1 degree of freedom the observed results are close enough to the expected results to assume the difference between the two is due to chance. The probability of obtaining these results is between 75% and 90%.

The null hypothesis (1:1 ratio female WT to male WT) is accepted. However, there is insufficent information to prove the experimental hypothesis true.

Categories# Observed# Expected(o-e)2/e
Female WT
Male WT
Male Y		43
22
23		50
25
25		0.98
0.36
0.16

Σ(o-e)2/2 =0.98 + 0.36 +0.16 =1.5
Degrees of freedom=# of categories -1= 3-1= 2

When X2 =1.5 and there are 2 degrees of freedom the observed results are close enough to the expected results to assume the difference between the two is due to chance. The probability of obtaining these results is between 25% and 50%.

The null hypothesis (2:1:1 ratio female WT to male WT to male yellow) is accepted. We may also except the experimental hypothesis (The parental Drosophila had genes of XyY and XX, with Xy being recessive to X. The genes expressed complete dominance and the trait is sex linked).



Conclusions / Explanations
It is apparent that in the course of this experiment there are some differences in numbers, for example, the expected results and observed results differed in the F1 generation. This and similar situations are caused by chance.
This experiment can be continued, some ways an aspiring scientist may wish to go about continuing this experiment are by finding which mutant traits cancel other mutant traits out.
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