Genetics: Drosophila fly eye color experiment.?

Question

i'm trying to figure out what kind of inheritance is being shown from the results of an eye color experiment in fruit flies.  wild type is a bright red eye color.  we crossed light orange eyed males with dark eyed females to get an F1 generation that was entirely wild type.  we crossed these flies with themselves and got an F2 generation showing wild type of both genders, dark eyes of both genders and light eyes that were all male.

i'm a bit confused because i know the flies have 7 genes responsible for eye color, lack some of them and you get a different eye color than the wild type.  so my guess is that the light eyed flies are missing certain genes, while the dark eyed flies are missing a different one.  i think that would explain why the F1 generation is entirely wild type.  I think x-linkage is also involved.  which may be the reason for the orange eyed flies in F2 generation are all male.

these are the phenotypes of F2 generation
wild type females = 357
wild type males = 161
Dark eyed females = 130
Dark eyed Males = 65
light eyed females = 0
light eyed males = 205
total:  918

i'm trying to find out where the genes for these traits are found, and if they are dominant or recessive.
please let me know what you think.

Anonymous · Accepted Answer

You are only looking at 2 eye colour mutants here, so any other eye colour genes are irrelevant, as they are not in the gene pool for this experiment.

You have picked up the important points. Whenever there is a class missing in females, you should suspect X-linkage.

Considering the light mutation only. If our cross were:

X+Xl x X+Y

Female offspring would be either X+X+ or X+Xl - all wild-type. This fits.

Male offspring would be 50% X+Y and 50% XlY. We have 161 + 65 non-light eyes and 205 light males which is 50:50.

For the dark-eyed phenotype, as both males and females show the double recessive phenotype, the cross should have been:
+d x +d

all offspring would have been ++ +d d+ dd. Not dark: dark 3:1.

Females not dark: dark is 357: 130 = 3:1

Males not dark: dark is 161: 65 about 3:1.

This is the most obvious explanation, but in doing 2 crosses which both affect a single trait i.e. eye colour, ideally we need to know the interaction - is one of these traits dominant over the other. I think from the data that the X-linked trait might mask the autosomal one.

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Genetics: Drosophila fly eye color experiment.?

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