Picture: X on left, Y on right

Was wondering why a X is so much larger than a Y sex chromosome?

because the y is a mutation and recesive chromasome.

Because the X carries more genetic information.

Dennis

don't know . are you going to tell us??

According to what I was taught in science class, the Y chromosome is simply an X chromosome that has undergone no fewer than 4 inversion mutations.  In an inversion mutation, parts separate and, well, invert themselves, then reattach.  In an inversion mutation, often sections are lost due to the breaking.  This eventually, over thousands and thousands of years, resulted in over 100 million base pairs being lost from the Y chromosome.

That is, if I remember correctly.  And I think I do.

sounds good

Wonder if they can compare chromosomes to preserved frozen ancient males, to compare the Y chromosome, to verify the gene mutation, or if its just a theory.

the mutations are as old as man, hence creating man. its not something thats happened since the two genders existed.

R

Found interesting related article talking about Y chromosome and DAZ and SRY genes.

QuoteIt wasn't always thus. Some 250 million years ago the Y was no different from any of our other chromosomes, which are distributed in our cells as 2 3 pairs. Today one of those pairs is made up of two sex chromosomes, which we know as the X and Y. Embryos that inherit two X chromosomes, one from each parent, develop into females. Those that inherit an X from their mother and a Y from their father become males. Originally, though, there was no Y and no X, just two identical chromosomes. The proto-Y was loaded with a variety of genes just like its peers, and it had nothing in particular to do with determining sex or making sperm. In fact, during this stage in our evolution, before mammals branched off from our reptilian ancestors, gender was probably determined by conditions in the environment (it still is in animals such as crocodiles and turtles, which have no sex-determining chromosomes). Then interesting things began to happen.

"A sex-determining gene arose," says Page. "An existing chromosome was somehow tweaked so that it became the decisive switch to determine the maleness or femaleness of the developing embryo. Perhaps a gene that used to be switched on by certain environmental cues became stuck in the on position, so the gene, rather than the environment, became the determining factor. All of a sudden we moved from a system in which whether an egg develops in shade or in sun determines if it's male or female, to hard-wiring gender into a chromosome."

That "tweak" could have been a spontaneous mutation of a gene already on the chromosome. Or a gene from another chromosome might have emigrated to the Y to take up a new function in a new neighborhood. Genes do that. No one quite understands how--it may involve faulty recombination--but over long periods of evolutionary time they may move aimlessly about the genome, occasionally finding a welcome home. Whatever the reason, suddenly the Y became different from its corresponding X. Now it harbored a brand-new gene, one unlike any other. And now it could no longer recombine with its former partner.

Recombination is the ace in the hole of evolution. When germ cells produce eggs in a woman or sperm in a man, their chromosomes are copied for inclusion in the nascent eggs and sperm; one set comes from the mother, one from the father. In this process, which is called meiosis, the chromosomes line up with their opposite numbers and sometimes swap genes. A swath of genes on a maternally derived chromosome number 3, say, may swap places with the corresponding bunch of genes on the paternal chromosome 3. Similar shuffling may occur in other chromosomes. That's recombination, and it has two chief consequences: first, it ensures variety in our species; and second, it allows us an opportunity to remain healthy by getting rid of bad genes. If one of Dad's genes is damaged, for example, there's a chance that it might be jettisoned for Mom's wholesome copy. In the long run, such random salutary switches prevail over recombinations that cause harm because embryos with healthy genes are more likely to develop into healthy, fertile people, while those with damaged genes may never even be born. As Page says, "Recombination is the fountain of youth for genes. It lets you do housecleaning along the chromosome."

QuoteUnlike all our other chromosomes, which bundle up a multitude of genes for many important and complex tasks, this sad excuse for a gene carrier seems to do nothing other than determine the male sex. Most researchers think that, like an appendix or little toe, it's well on its way to becoming extinct--eventually humans will just have to determine gender some other way.

From discovery magazine http://findarticles.com/p/articles/mi_m1511/is_n11_v18/ai_19847181?lstpn=article_results&lstpc=search&lstpr=external&lstprs=other&lstwid=1&lstwn=search_results&lstwp=body_middle

HAHA. WE ALL GONNA BE MITOSISHEADS!