Y Chromosome Isn't Defective Afterall

[Tsukuru]

Male Chromosome Map Shows Men Go It Alone (http://abcnews.go.com/wire/SciTech/reuters20030618_413.html)

If you've ever taken any sort of biology course, then you know that the Y chromosome, found only in males, is greatly inferior to the X chromosome. The recent findings showed that the Y chromosome can repair itself without relying on the other chromosome as X chromosomed do in women.

For those who don't know each person has two chromosomes, males having X Y and females X X. The Y chromosome is considered inferior because when the genes from mom and dad are put together it gets all of the 'bad' genes that cause defects.

[ShadowTiger]

Wow. No wonder I wanted to be a biologist when I grew up. Heh. Good to know, I guess. :laughing:

[plith]

Actually, I was led to believe that Y is supposed to be inferior to X because in all cases on those two chromosomes that decide any non-sexual trait, the X chromosome is considered dominant. "Bad genes"?

[Tsukuru]

Well that's what I meant. The Y chromosome receives all of the recessive genes. If the X chromosome also by chance has the recessive genes the negative characteristics will show up in the person.

[Jigglysaint]

Well if I remember correctly, an X chromosome is a carrier, meaning that more often than not, a person has the bad gene, but doesn't show it. The Y, which isn't passed(I think) is what causes then genes to show. I'm mostly wrong however.

[Ich]

If you don't care about what I learned in Bio, skip this entire post.

The Y (often) doesn't do anything. The X has recessive and dominant traits, and the Y does not. When it comes to determining if someone has an X linked genetic defect, the Y is ignored completely. If the man has an "X" (dominant) then that shows up, and if he has an "x" it is recessive. If a woman has an "XX" or "Xx" or "xX", she receives dominant traits. "xx" is the only possible way for a woman to receive a recessive trait. Colorblindness is one of the main X-linked genetic defects, and men have it far more frequently than women. Also, a defective male can only pass on defective traits, while a "Xx" female can pass one only one of the traits, either "X" or "x."

Punnet Squares help with this concept.




x y
__________
X | Xx | Xy |
|-----+----+
x | xx | xy |
¯¯¯¯¯¯¯¯¯¯

For explanation, box #'s are as follows:
12
34


The man is on top, with x y distributed evenly among the four possible offspring (the boxes) the female is on the left.

The woman's X goes to box 1 and 2, the man's x goes 1 and 3.
The man's y to 2 and 4, and the woman's x to 3 and 4.

The outcomes are a carrier woman, and unaffected boy, an affected girl and an affected boy.

[inori]

The main "problem" with the Y chromosome is that it is significantly smaller than the X. Put simply, it doesn't have all the genes that its partner, the X chromosome, does.

Think of it this way:
- Gun X (which in this analogy is the normal X chromosome) is fully functional. If you have at least one gun X, you can hit the target.
- Gun x (which is an X chromosome carrying a sex-linked trait, say color-blindness) is defective; the sights aren't aligned. You can't hit the target with an x gun.
- Gun Y (which is a Y chromosome) is missing the trigger, the hammer, and half of the barrel. Oh, and the bullets. Asking whether gun Y can hit the target is irrelevant; gun Y can't even fire.

Girls get two X chromosomes, so they have two chances to hit the target. Guys get an X and a Y, so they only have one chance... if their one X chromosome has a sex-linked gene, they'll "miss the target."

[TheGeepster]

I did hear something interesting about the Y-chromosome, traditionally thought of as holding junk. Apparently a researcher found that the Y-Chromosome does have ability to repair itself due to a palindromic nature.

Can't verify that though. Something tells me genetics can get very hairy with some of the more complicated aspects, although on it's simplest level, it's merely a matter of relatively simple probabilities.