OT: Colorblindess (was Re: [TriLUG] Mandrake/Redhat usability.)

[Joey O'Doherty]

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No, the gene is actually on the X chromosome.

Colorblindness is an X-linked recessive trait. Recall that (normally)
with a recessive gene you need a copy on each chromosome for the the
recessive phenotype to be expressed.  If the other chromosome has the
dominant gene, you don't express the recesive phenotype.  This is the
case for females with colorblindness: they must cary the colorblindness
gene on both of their X chromosomes in order to express the phenotype.
This is why there are so few of them.

However, males only receive one X chromosome.  Its counterpart is the Y
chromosome.  Think of the Y as an X with a missing leg.  The
colorblindness gene is on that missing leg!  So if a male has an X
chromosome with the colorblindness gene, it will always be expressed
because there is no chance for it to be overridden by the dominant gene
on the other chromosome.  The Y chromosome simply doesn't cary that gene.

This is why colorblindness and other X-linked traits (baldness?) are
always passed down from mother to son.  Men simply cannot pass the
X-linked gene to their sons, only to their daughters.

</lesson type="genetics">

James Manning wrote:
|>[Jeremy Portzer]
|>(For females it's only about 0.5% of the population due to
|>the X-linked nature of red-green colorblindness.)
|
|
| s/X/Y/ ?


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