Oh, Lord, send me biologists.

From the tiny bit I learnt about punnet squares in high school biology, yes! entirely feasible! As I understand it, quite probable, as the dominant genes are the black hair and the green eyes (green is a deriviative of brown).

Anyone else, feel free to shoot me down in flames on this one!

Very feasable. Black hair is dom. and blue eyes recessive....to put it simply.

It's possible. Here's a link for eye color calculation, which is trickier than the hair.

According to high school biology, my daughter shouldn't have green eyes, but genetically, it is possible (dad and mom have blue eyes)

It boils down to a dominant gene mutation (I think) There is a fairly good explanation here: http://www.techmuseum.org/exhibits/online/ugenetics/ask.php?id=29

Amy

Eye color is a bit more complex than a high school biology course can delve into. Last I read there were at least 8 genes identified and they aren't all straight Mendellian inheritance patterns with a simple "dominant" and "recessive" characteristic. There are some with partial penetrance and of course how light reflects off certain backgrounds such that things not directly related to the eyes can influence perceived color.

She_wulf said:

According to high school biology, my daughter shouldn't have green eyes, but genetically, it is possible (dad and mom have blue eyes)

It boils down to a dominant gene mutation (I think) There is a fairly good explanation here: http://www.techmuseum.org/exhibits/online/ugenetics/ask.php?id=29

Amy

Click to expand...

Is it a single gene? Is it dominant, so it only needs to be on one X chromosome? Does it need to be on both? If it's only on one X chromosome the niece would have had to get it from her father. If it needs to be on both, well, she still needs to get one from her father but could get one from her mother.

About the hair? That's not simple either. Consider that hair color isn't an either/or category. It's not like you have either blonde hair or black. There's a scale. Or possibly two scales: the amount of pigmentation and the amount of red.

Now, I know for sure that kids with one black-haired parent and one brown-haired parent can have black hair, but I think with one blonde parent and one black-haired they'd end up with (at most) very dark brown. Some of the lack of pigmentation would show.

Oh so it's not sex-linked at all? I thought it was from your initial description.

This explanation here says that it's possible to be a carrier. So yes, the niece can have it.
Basically that means that the character's sister has balanced Robertsonian translocation (carrier) and her daughter gets either the monosomy or the trisomy thereby. I'm not sure what the physiological effects of those are and how they're different. The sister could also have carrier or normal kids. This is all assuming the sister's husband is normal.

Argh!

Argh!!! I just typed you a long, detailed reply and it disappeared when I clicked "Submit Reply." *sigh* Here I go again . . .

Had to reply to this post. I have a Master's in genetics. Short answer to your rob translocation question -- the niece is only at risk of having inherited the translocation if her parent also has it. Robertsonian translocations don't "skip" in families.

Long answer: First of all, a Robertsonian translocation (rob(t)) can be associated with infertility, but not all people with a rob(t) will be infertile. So, rob(t) definitely does not equate with "permanent and incurable infertility." Second, a "carrier" of a rob(t) is COMPLETELY different than a carrier of a single gene disorder like cystic fibrosis or sickle cell anemia. rob(t) is chromosomal (the large packages that the genes are arranged on) not single-gene (the individual instructions for how our bodies work).

A "carrier" of a rob(t) is someone who has a balanced rob(t). This means that they have all of their genetic information, but it is arranged differently than usual. Someone with a balanced rob(t) has two chromosomes connected together and, as a result, they have 45 total chromosomes instead of the usual 46. A balanced rob(t) does not cause birth defects, mental retardation or any obvious differences in that person -- many people with a balanced rob(t) have no idea that they have it. The main problem with a balanced rob(t) is that that person is at risk of having pregnancy losses or children with birth defects and/or mental retardation. This is because the person with the balanced rob(t) can pass on 1) their normal copies of the chromosomes resulting in a chromosomally normal child or 2) their balanced translocation, resulting in a healthy child with a balanced rob(t) or 3) no copy of one chromosome, resulting in a pregnancy with a monosomy which is usually embryonic lethal or 4) the translocation plus the normal copy of the chromosome resulting in a pregnancy with an unbalanced translocation. Depending on the chromosome involved, the extra information from the unbalanced translocation might cause death in utero or might result in a child with birth defects and/or mental retardation.

I hope this makes sense -- it's a bit complicated to explain without visual aids!