A dihybrid cross is performed in Drosophila - one parent is heterozygous for both genes (B/b ; F/f) and is test-crossed with a homozygous recessive type (b/b ; f/f). (where B = black body; b = brown body; F = forked bristles; f = unforked bristles.)

The results are:

black, forked 230

black, unforked 210

brown, forked 240

brown, unforked 250

How many degrees of freedom would you use in this case?

What would be the expected number for each phenotype?

Calculate the chi-square value for this cross.

Assuming p=0.05, what critical value would you use to compare the calculated chi-square value against?

Do you reject or not reject the expected ratio in this case