Chromosomes

[Jo-D]

I have been thinking about the following questions, any assistance is much appreciated!
1) why is that human embryos with 3 copies of chromosome 1 (ie extra copy of chromosome 1) die, yet adults with an extra Y-chromosome are perfectly healthy?

2) how do you distinguish whether a karyotype is lethal or not and the sex of the individual with that karyotype? say: 45, X or 69, XXX

Thanks!

[Poison]

Chromosome abnormalities can be tolerated to a point. If this is on sex chromosomes, they are often tolerated.(There must be one X present. you can not have a YO zygote alive- but well this is very rare .) The individual is not normal but can live. Also some autosomal chromosone abnormalities can be tolerated too. Like 21.chromosome trisomy (leads to down sydrome).

I couldn't understand your second question.

[Jo-D]

sorry um i didnt quite understand, i get the first part of the first question, but yeh y is it that extra Y chromosome dont have a major effect where as an extra chromosome 1(i assume they mean X chromosome right?)

[Poison]

You can think like sex chromosomes are not that important compared to others. But X is important, no zygote can survive without X. From a point you can think that X is more important that Y for the organism to survive.
Extra Y does not have a major effect? XYY leads to Supermale syndrome(Also known as XYY trisomy or Jacob's (hope I remember right) syndrome). Yes, XYY male looks normal, but if I don't remember wrong, they are usually more agressive and some scientist say they have more tendency to commit a crime.
From another point of view, (actually this is my comment), if you think about XXY, XX is female and XY is male, having XXY is a situation like not being able to decide being female or male. If you have a look at XYY, XY is male and YY is nothing. So the person is obviously male.
I don't know if it helped or not, but hope it did.

[scottyiu]

So is it possible to have a Y and none or YY?

[Poison]

Theoritically yes. But you usually do not recognise if that happens because the growth does not go any futher.

[scottyiu]

So are you saying that anyone with YO or YY won't really survive very long?

[Poison]

survive? No. Probably die after fertilization.

[mith]

how would you have a YY embryo???? A sperm can't fertilize itself....

[scottyiu]

But then how do you get XYY anyway? two sperm plus an egg?

[Poison]

No,
A sperm carrying XY (they are not seperated), and an egg.

XY+X=XXY

Or
An egg carrying XX (not seperated again), and a sperm carrying Y.

XX+Y=XXY

[Poison]

how would you have a YY embryo???? A sperm can't fertilize itself....

Yes, I was talking about YO sorry, I didn't see that.