DROSOPHILA DIHYBRID CROSS

Question

I did a cross between Wildtype wing shape, hairy bristles female and vestigial wings, wildtype bristles male. All the F1 progeny was wildtype as expected. The F2 also showed 9:3:3:1. The chi square value on the other hand rejected the null hypothesis that the the values should be 9:3:3:1. Not sure what error i may have made

Answer 1

It looks to me like you are assuming the wildtype traits are also homozygous, which they may not be. If they are not homozygous for both traits, then you also cannot expect the F1 offspring to all have the same phenotype/genotype which would change your expected ratio for the F2 offspring. It is not clear if you are using actual lab data, a simulation, or a data set to compare to the expected, but also consider the element of chance in genetic crosses. Additionally, if your assumptions on the setup are correct, I would check that you are using the correct critical value and degrees of freedom for the chi square test. As a last potential explanation, are you sure each of these traits follows a Mendelian pattern of inheritance to get the anticipated ratios you are using?