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Old 09-06-2009, 06:47 PM   #1
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Default Chromosomes

Ok so I took some first year university biology several years ago, and I've forgotten most of it. My wife asked me a question regarding my daughters traits, etc, and I started thinking about chromosomes again. So here's my question:

During sexual reproduction, I know that the women and man contribute one chromosome. The man either gives an X or a Y, and the women can only give X chromosomes. Because I have a daughter, she would have had to receive an X from me. Where my question comes in is with the crossover phase in Meiosis. During my male meiosis, does my Y chromosome cross with the X chromosome? If that is the case, that would mean that both traits from my fathers Y chromosome and mothers X chromosome are present in the X I gave to my daughter? I'm pretty sure that is the case, but I'm not 100%. I'm pretty sure I don't just replicate the X and Y because I'm a male and send those out as direct copies.

Thanks folks, just something that's been bother me that my old text book didn't answer for me.
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Old 09-06-2009, 07:38 PM   #2
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This is what I read. I’m not sure if it is entirely correct.





Crossover does not occur in the sex chromosomes. Females inherit and X chromosome from there mother and a x chromosome that is technically that of there father’s mother.



Each person normally has one pair of sex chromosomes in each cell. Females have two X chromosomes, while males have one X and one Y chromosome

Y chromosome


The Y chromosome is the Sex-determination system chromosome in most mammals, including humans. In mammals, it contains the gene SRY, which triggers ******** development, thus determining sex....
. Both males and females retain one of their mother's X chromosomes, and females retain their second X chromosome from their father. Since the father retains his X chromosome from his mother, a human female has one X chromosome from her paternal grandmother, and one X chromosome from her mother.



Problems occur when recombination does occur.
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Old 09-06-2009, 08:45 PM   #3
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I know for sure that crossover occurs in the sex chromosomes, in fact, that's like the only place it occurs. Without it there wouldn't nearly be as many variations. Judging by this info I found, it appears there is crossover between the x and y chromosome in meiosis:
There are very few genes found on the Y chromosomes.It is incorrect to say
that the Y-chromosomes contain all the genetic information as the
X-chromosomes.
The end region of the X & Y chromosomes are common; i.e. the same genes are
present in this terminal region. Because of this small region of homology
shared by both the sex chromosomes, synapsis can occur between X and Y
chromosomes in this region during prophase I.
The inheritance of these genes is similar to that of an autosomal gene,
therefore genes located at the terminal region of the sex chromosomes are
called pseudoautosomal genes. To date, 9 peseudoautosomal genes have been
found.
With reference to your question about the different sizes of the sex
chromosomes, the pseudoautosomal region of the Y chromosomes helps in
pairing of the X and Y chromosomes during meiosis.
Hence, males have 2 copies of the pseudoautosomal genes, one in the
terminal region and one in the corresponding region of their X chromosomes.
In females, their X chromosomes pair up during prophase I and then
separate, giving rise to eggs bearing single X chromosomes.
For your information, scientists have discovered 20 genes outside the
pseudoautosomal region. One of the most important genes is the SRY
(sex-determining region Y) gene. In the presence of this gene, an embryo
develops into a male and in the absence of it, you will get a female
embryo instead.
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Old 09-06-2009, 10:57 PM   #4
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My degree is in cell biology but I'm in cancer research and haven't studied this stuff in about a decade LOL. But yes, there is recombination between X and Y in male meiosis. Your daughter will have the X you donated, and the genes on it will be mostly from your mother with a little of your Y sequence due to some recombination in the pseudoautosomal region. If you have a son, the Y you donate may have some sequence on it from your X (which you got from your mother) due to recombination in that region. But there is a more interesting aspect that hasn't been mentioned yet.

Females have two X chromosomes, but don't transcribe twice as much of the genes present on X as males do, due to the phenomenon of X inactivation. One of your daughter's two Xs, either yours or your wife's, is inactivated in every cell. This occurs very early in ebryogenesis. In mice it happens in the 2 or 4-cell blastocyst but in humans it's just a bit later, 16-32 cells IIRC. Which X is inactivated is random- not all 16 (or 32, whatever) cells will inactivate your X and not all will inactivate your wife's. But inactivation of that X is irreversible and persists in all daughter cells descended from each of those 16 or 32 cells for the life of the organism. So your daughter has groups of cells where the X is entirely from you, and other groups of cells with your wife's X. This results in mosaic gene expression, the patchy coat color of calico cats and all that ****. The molecular biology of X inactivation is kind of interesting.

Last edited by ScottFW; 09-06-2009 at 11:09 PM.
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Old 09-06-2009, 11:09 PM   #5
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Quote:
Originally Posted by ScottFW View Post
My degree is in cell biology but I'm in cancer research and haven't studied this stuff in about a decade LOL. But yes, there is recombination between X and Y in male meiosis so your daughter will probably have some sequence on the X you donated that came from your mother. But there is a more interesting aspect that hasn't been mentioned yet.

Females have two X chromosomes, but don't transcribe twice as much of the genes present on X as males do, due to the phenomenon of X inactivation. One of your daughter's two Xs, either yours or your wife's, is inactivated in every cell. This occurs very early in ebryogenesis. In mice it happens in the 2 or 4-cell blastocyst but in humans it's just a bit later, 16-32 cells IIRC. Which X is inactivated is random- not all 16 (or 32, whatever) cells will inactivate your X and not all will inactivate your wife's. But inactivation of that X is irreversible and persists in all daughter cells descended from each of those 16 or 32 cells for the life of the organism. So your daughter has groups of cells where the X is entirely from you, and other groups of cells with your wife's X. This results in mosaic gene expression, the patchy coat color of calico cats and all that ****. The molecular biology of X inactivation is kind of interesting.
Thanks so much for that awesome explanation! I knew miata turbo.net wouldn't let me down

P.S. - Envious of your work.
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