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  © This page is Copyright Justin Hutchings, 2001. Do not duplicate without express permission from the author.

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

Punnett square for F1 generation F\M Xy Y X XXy XY X XXy XY

Female Male Parent WT Y F1 24 WT 25 WT F2 43 WT 22 WT 23 Y

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. The null hypothesis: A 1 female WT:1 male WT ratio will be observed from the parental cross.

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.

Punnett square for F2 generation F\M X Y Xy XyX XyY X XX XY

Female Male Parent WT Y F1 24 WT 25 WT F2 43 WT 22 WT 23 Y

The null hypothesis: A 2 female WT:1 male WT :1 male yellow body ratio will be observed from the F1 cross.

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 X^yY and XX, with X^y being recessive to X. The genes expressed complete dominance and the trait is sex linked).

All material on this page was developed from the format provided by resource 1.