Drosophilia eye color

[born2ride]

Can someone PLEASE tell me "What evidence led Morgan to hypothesize that the gene for eye color in Drosophilia is carried on the "X" chromosome?" Could you also 'use' a Punnett square to show me? I have a bio exam and I don't understand it. Thanx. <3

Arggh!

[Winter]

Morgan concluded this thru several experiments.

> He found a white eyed mutant male drosophila among the normal red eyed kind.
> He crossed this with a red eyed female.
> The F1 generation produced no white-eyed offspring.
> Then he crossed the males and females of the F1 generation and 50% of the produced males had white eyes.

-Males have an X chromosome and a Y chromosome
-Female have 2 X chromosomes

The gene for white eyes is on the X chromosome. The Y chromosome has few genes.
Males have only one copy of this gene therefore they express what the X chromosome specifies.

So, a X(w)Y male has white eyes.

The gene cannot be on a Y chromosome, because a cross between
a heterozygous female [ X(w)X ] and
a white eyed male [ X(w)Y ]

will produce some white eyed females [ X(w)X(w) ]

hope this helps...

[born2ride]

That helps a lot! Thanx! <3

[Winter]

no problem, glad to help