The item of news that jumped out at me on BBC radio last night was that 99% of our genes have close counterparts with mice, and 80% of them are identical. Nine thousand new mouse genes have been discovered and 1,200 of these are now identified to be the same as human genes. John Steinbeck must be chuckling somewhere in the informational universe.
The latest issue of "Nature" contains the first draft of the mouse genome. This has been produced by the Genome Project at Cambridge in England, though a private US company had already cracked the code (and I have a vague memory that a Chinese research group have also done so quite recently). However, the Cambridge results are now publicly available on the Net. In short, the mouse genome is contained in 20 chromosome pairs (cf 23 in humans) containing 2.5 billion nucleotides (the "letters" of the code -- 2.9 billion in humans) and, altogether, has about 30,000 genes -- about the same number as humans. The fact that we only have about 30,000 genes was humbling news some two years ago when the draft of the human genome was first announced. Most geneticists were expecting at least 60,000 genes and some, 100,000. However, "our" set of 30,000 genes produces many times more proteins in our body (and a more complex brain) than the almost identical set of mouse genes, so there's obviously much more involved than just the genes themselves. This is the big mystery that now faces geneticists. There are many genes -- such as those responsible for blood pressure and bone growth -- that carry out almost identical functions in both mice and humans. These genes have hardly changed in the 75 million years that have elapsed since we shared a common ancestor which co-existed with the dinosaurs. But caution must be exercised is assuming this for all genes which are similar in both mice and men. For example, we still have the same genes that produce tails in mice. Is it that they're simply repressed in our case? More likely, they are now used for entirely different purposes. However, the genes that are responsible for immunity in specific environments or for sexual activity or for basic life-and-death situations have diverged very markedly in the same period according to the uniquely different trail of environments along which mice and humans have experienced entirely different sorts of survival crises. Discovering the function of individual human genes by means of noting what their equivalent (or identical) genes do in mice or other creatures can't be relied upon in a straightforward way. The proteins these genes produce may be similar or even identical to those of mice -- but carry out entirely different functions in man. It seems to me that gene therapy, much flaunted in the prospectuses of newly-launched biotechnology companies, is going to take a backward seat for a long time to come until more is known about the interaction and permutations of individual genes at the stage of protein synthesis. This will depend on more precise knowledge of what used to be called "junk DNA" -- the very long strings of apparently nonsensical DNA that supposedly merely linked the genes like the cable between the lights on a Christmas Tree. The interconnecting stretches of junk DNA are now more respectfully termed "introns" and it's now being realised that they have a curious, repetitive type of pattern which may be significant but not yet understood. Introns with abnormal sequences seem to be associated with diseases that were hitherto considered to be due to faulty genes alone. It is probable therefore that introns are important in determining the way that single genes from different parts of the chromosome are actually brought together in different ways in order to make different proteins. Proportionately, humans have far more intron DNA than mice, so -- to those who worry about these things -- our superior status has been restored! Thorstein Veblen would have been amused by this. All this new complexity means that mankind is not going to safely manipulate many human genes for therapeutic (or eugenic) reasons for a long time to come -- at least until introns are thoroughly understood. For this, the study of simpler creatures, such as bacteria, with much smaller numbers of genes and introns, is going to be more important in the years immediately ahead. Keith Hudson ---------------------------------------------------------------------------- ------------ Keith Hudson, General Editor, Handlo Music, http://www.handlo.com 6 Upper Camden Place, Bath BA1 5HX, England Tel: +44 1225 312622; Fax: +44 1225 447727; mailto:[EMAIL PROTECTED] ________________________________________________________________________
