On Tue, 5 Dec 1995, Alvaro Jaramillo wrote:

> >
> Now this makes more sense, I knew I had something wrong. By virtue of being
> on the X chromosome the feature is expressed in males since they don't have
> another X chromosome that may have the gene that overrides the expression of
> colour blindness. Women on the other hand are less likely to show the trait
> since it would be expressed only if it is carried by both X chromosomes as
> the trait is recessive. Now is this right?
>

That is right. The female who does express green-red colorblindness is a
rare creature (if 1/100 males are G-R colorblind, then 1/10,000 females
will be, since they need to stumble onto that 1/100 allele twice at
once. Barring incest :-)). If you know a female in that category (I do),
then you can tell her that all her male children will be colorblind, and
all her female children will have normal vision, but be carriers. But
chances are she already knows that.

Chris Hill
Everett, WA
cehill at u.washington.edu