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    • Waste- or Wonder-Land?

      If you've followed the news over the last few years, you'll know that we humans have just about mapped our own DNA. Now the big difference between Boy- and Girl-DNA is that one of the chromosomes is different - boys have a Y-chromosome, while girls don't. For a while the scientists thought that the tiny Y-chromosome was relentlessly headed for oblivion, and that it would be gone in a few million years. But the latest research shows that for all its faults, the Y-chromosome (and its nasty byproduct, boys) is probably here to stay.

      Just about every cell in your body has the entire DNA needed to make another you. Our DNA is lots of things at once - it's a blueprint for making a human being, it's a history book of our ancestry, it's a giant medical book, and it's a whole lot more.

      When a cell gets ready to split into two, the DNA also prepares to split itself into two. The 2 to 3-metre length of the DNA bunches itself up into 46 little packages. We call them "chromosomes" because as early as 1848, the geneticists would colour them with various dyes, to show up various features - and "chromosome" means "coloured body".

      If you look at these 46 chromosomes with a microscope, you'll see that 45 of them are the same in boys and in girls, but that the 46th chromosome is different. It's quite large in girls where it carries about 1,500 genes, but in boys it's tiny, and carries only 78 genes. So guys, next time you go thinking that you are the Lord of Creation, just remember that your pulsating masculinity is made possible by just 78 genes. In fact, you can think of women as the luxury model with all the options, while guys are the cheap economy model without the air-con, power steering and cruise control.

      Women have an advantage with their chromosomes 45 and 46 being big bold matching X-chromosomes.

      You can understand this advantage if you think about constructing a building from the architect's plans. Now suppose that the plans have been made harder-to-read by smudges, burger stains and spilt coffee. It would be very hard to complete your building with these damaged plans. It would be very handy to have a spare undamaged set of plans.

      Chromosomes 45 and 46 provide a spare set of plans for each other. The fertilized egg uses these plans as a blueprint as it grows itself into a baby human over 9 months.

      If one X-chromosome has a damaged section, the growing embryo in the uterus can use an undamaged section from the other X-chromosome as it builds itself.

      But boys can't do this. After all, while their chromosome 45 is a big boofy X-chromosome, their chromosome 46 is a minuscule Y-chromosome. The Y-chromosome doesn't have a matching partner. If the Y-chromosome is damaged, it can't read the X-chromosome next door to find an undamaged section.

      So the Y-chromosome looks like a disaster waiting to happen. And indeed, boys suffer quite a few diseases (such as red-green colour-blindness) that girls don't get.

      But the news gets worse for the pathetic little Y-chromosome.

      It mutates very rapidly, about 1,000 times faster than any other chromosome. It seems that it was virtually identical to the X-chromosome about 300 million years ago. In fact, there are a few short sections on the very ends of the Y-chromosome that are identical to the very ends of the X-chromosome - but over 95% of the Y-chromosome is very different from the X-chromosome. It has mutated massively. Over the last 300 million years, the once-proud Y-chromosome has shrunk from about 1,500 genes to its current miserly 78 genes. And if it keeps shrinking and mutating at the present rate, it'll be totally useless in just a few million years.

      Yup, for a while there, the scientists really thought that the Y-chromosome was a regular wasteland.

      But in June 2003, Nature published some reassuring research by Dr. Page from the Massachusetts Institute of Technology, which turned the Y-chromosome from WasteLand to WonderLand. He and his team worked out, after a lot of very hard work, that the Y-chromosome has a special trick, which means it doesn't need a matching partner to cover for any damaged sections (or bits).

      They discovered that large sections of the Y-chromosome are "palindromes". You might remember from your high-school English days that a "palindrome" is a word, or phrase, that reads the same in each direction. The word "radar" is a palindrome, as is the word "level".

      It is very exciting that sections of the Y-chromosome are palindromes. It means that if one section of the Y-chromosome is damaged, sometimes it can find an undamaged version of the same section somewhere else in the Y-chromosome. It can ignore the damaged section, and use the undamaged section somewhere up at the other end of the Y-chromosome.

      But while this is good news, it is also a little disturbing. Yes, the Y-chromosome can fix itself up - but only by having sex with itself...
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