X and Y chromosomes vs. dominant/recessive genes

[DaveC426913]

Been long time since my high school biology. I know about XX/XY chromosomes, and I know about dominant and recessive genes, but I'm a bit rusty about the connection.

If father has brown eyes, and son has blue eyes, it is a foregone conclusion that father has a brown-eyed X and a blue-eyed Y? That's the only way the son could be blue-eyed, right? Because he must have gotten his Y from his father, and it must have been blue.

 

[rootone]

I think that is approximately correct, but eye color is not encoded entirely by just one gene in the XY chromosome.
Other genes may influence the phenotype (the actual development and appearance of eye coloration).
Those other genes may be expressions of another chromosome pair, not the XY one.
Humans have 23 chromosome pairs in total.

You might find this interesting.
https://en.wikipedia.org/wiki/Chromosome

 

[DaveC426913]

Hm. It seems to be much more complex than in High School.

http://genetics.thetech.org/how-blue-eyed-parents-can-have-brown-eyed-children

 

[BillTre]

I vaguely remember a brown-blue dominance relationship from high school, but apparently it is more complex. The references about more complex genetics here come from post 2000.
Apparently eye color is based not just on particular pigments but also light scattering phenomena.

I don't remember anything about eye color and X-linkage, but the main color blindness genes are on the X-chromosome and color blindness is much more prevalent in male than female humans. There are a limited number of photoreceptor genes. They are found on the X-chromosome, but not on the Y-chromosome. These genes produce proteins that absorb light and lead to changes in receptor cell neural signals.

Males only have the genes on one X-chromosome. Any defective gene on that chromosome are revealed in the males carrying it because the males don't have a second chromosome carrying any alternate genes that could produce a more functional product. Females would have to have two copies of a defective gene to have an equivalent condition, a statistically less likely situation.

The wikipedia article says there are bunch of other genes affecting color vision (but they seem minor (not common? or weak affects?)). They could affect optical components like the lens (perhaps filtering the light before it gets to the receptor cells) or cell types and neural connections (affecting vision processing by neural cells). Details unknown to me.

 

[DaveC426913]

Unrelated: BillTRe: what kind of fry is that in your avatar?

 

[BillTre]

It's a larval relative of zebrafish, Devario annandalei. Closer to a giant Danio than a zebrafish.
I accidentally got something like a phase contract effect.
There are microworms and rotifers (food items) around it.

 

[DaveC426913]

It's a larval relative of zebrafish, Devario annandalei. Closer to a giant Danio than a zebrafish.

Love zebra danios. Very active tank denizens. Really liven up a tank. Never had giant danios tho.

There are microworms and rotifers (food items) around it.

Wondered if that's what I was seeing. Cool.

 

[BillTre]

Giant danios (and annandalei) are bigger and more active. Require larger tanks.

 

[Fervent Freyja]

This has changed since you were in high school. The old Mendelian model for inheritance of eye color has been replaced, although you can still find it being used, it really isn't accurate. It's no longer believed that the colors are recessive or dominant. A many number of genes have been found responsible for eye color. Those genes aren't located on sex chromosomes, see chromosome 15 (most responsible are found here). Genotype–phenotype associations and human eye color is a good read on the topic.

Eye colors can "mix". My husband is brown-eyed, while I'm blue-eyed, but our daughter has a mixture of both; for now, the outer circumference of her eyes are brown and the inner blue.

No telling how many scandalous accusations have went on by going by that model! I remember being highly suspicious of some blue-eyed friends with brown-eyed parents. Turns out that it's more complicated than looking at punnet squares!

 

[DaveC426913]

Yeah, that's what I was trying to figure out with my wife, based on her family's various eye-colours going back to her great-grandparents. We'd worked it out to a paradox and had to stop.

We were on vacation, so no internet verification, and I was only 98% sure it was as straightforward as we were once taught.

This thread is the remaining 2%.

 

[Fervent Freyja]

This essay discusses the probability of eye color inheritance and takes into account great-parents eye color too. A more thorough paper: https://www.researchgate.net/publication/221869058_Prediction_of_Eye_Color_from_Genetic_Data_Using_Bayesian_Approach