news.bbc.co.uk/1/hi/sci/tech/3000742.stm
X and Y chromosomes, SPL The X chromosome (left) dwarfs the Y (lower right) This DNA bundle - one of 24 distinct chromosomes found in human cells - holds the crucial information to make the male of our species. The work is part of the enormous job of following up the data that came out of the international Human Genome Project (HGP). The results provide important insights into how humans evolved and may explain how some kinds of infertility occur. The work of refining this DNA sequence to higher levels of accuracy was declared complete in April. Any attempt to make sense of the data inevitably involves large-scale computing effort, but, by any standards, annotating the Y chromosome was a huge task. The Y chromosome contains a great many repeated sections of DNA and far fewer genes, letter for letter, than other chromosomes. Sperm production Francis Collins, director of the US National Human Genome Research Institute, said in Washington DC on Wednesday that the Y was the fifth chromosome of the completed human genome sequence to undergo detailed analysis. HANDBOOK OF THE MALE Graphic, bbc Men have an extra brain gene 44 Read more The scientists found 78 genes in total on the Y, many but by no means all of them to do with sperm production. One is the sex determining gene, the "master switch" that makes a baby boy; For every million letters of genetic code they looked through, the researchers found only three genes, far fewer than the 10 per million average throughout the rest of the genome. The chromosomes in the nuclei of our cells are arranged in pairs (females have two copies of the much larger X, while men have an X and a Y). Gene fixing Researchers say the chromosomes draw on their mate to carry out repairs to genes that suffer mutations through disease or replication errors. THE HUMAN GENOME The double-stranded DNA molecule is held together by chemical components called bases Adenine bonds with thymine ; It will use one copy to fix a flaw in another - a process called gene conversion. Dr David Page, from the Whitehead Institute in Massachusetts, who led the team deciphering the Y chromosome, said: "The sex chromosomes represent a grand experiment of nature. He said doctors were already using his team's data to understand the genetic origins of male infertility. He added that genes on the Y might play a role in influencing gender-specific differences in disease susceptibility. The Y chromosome work is reported in the journal Nature.
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