Gene questions - eyesight and color

I am one of 4 children. My mother has brown eyes and has good-to-slightly far-sighted vision. My father has blue eyes and is near sighted.

3 of us (myself included) have blue eyes and are near sighted.
My brother has brown eyes and has good-to-slightly far-sighted vision.

I understand (from my 1 semester as a statistics major), that 4 isn’t a large enough sample size, but it’s more than children than most people have.

Let’s say, VERY hypothetically speaking, that my parents had 100 children.

1.) Would ~75 have blue eyes and be near sighted, and ~25 have brown eyes and be far-sighted?

2.) I believe that blue-eyedness (?word?) is a recessive gene, so perhaps ~75 would have brown eyes. Is this the case?

3.) Would there be some children who were blue-eyed and were far-sighted, and some who were brown-eyed and near-sighted, or is color and seeing ability tied together? (At least in my family. I’m sure that brown-eyed-near-sighted people exist, so I don’t think that they’re tied together universally; but are they tied together in my family?)

Thanks,
Rucksinator

I don’t know that there is any direct linkage between near-sightedness and eye color, so I can’t answer that.

Given that blue eye color is a recessive trait, we know that your father’s genotype for eye color is bb. Where there are children of your parents with blue eyes, we also know that your mother’s genotype is Bb, so, this is the Punnett square (please forgive the crude graphics) which shows the possible genotypes for your parents’ children:



|--b---b--|
B  Bb  Bb |
|---------|
b  bb  bb |
|---------|


So, there would 50-50 chance of blue eyes in this generation.

It is not so simple. Iris color is not monogenic (there is more than one gene controlling it), nor does it only have two alleles at every locus (gene), and the alleles at each gene can be partially dominant. This lets people have a range of eye colors from nearly black through to browns, hazels, greens, and blues. It is true that blue is generally recessive at the major eye color locus, but it is not always the case. This is why my mother has hazel eyes, my father has green eyes, my brother has brown eyes, and I have blue eyes.

These have no relation to refractive error, which is based not on iris color but on eye shape and lens shape. I can ask my wife (an optometry student) if there are any differences – perhaps lighter eyed people are more sensitive to light and perhaps less able to compenate for refractive error, or perhaps there is a genetic linkage. But, the relationship doesn’t hold up in my family – both of my grandfathers have blue eyes and nearly no refractive error. My mother has hazel and a large astigmatism. My father has green with virtually no error. My brother has brown and no error and I have blue with a large astigmatism and myopia.

The actual rate of nearsightedness (as opposed to mere predisposition to it) is not particularly strongly associated with genes. The rate of myopia can change dramatically from one generation to the next. See Cecil on Will sitting too close to the TV ruin your eyes?

Nothing biological ever is, is it? :slight_smile: I should know better than to trust my unexercised memory!
This site explains eye color genetics pretty succinctly (simplified, of course).