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2junk dna does have a use。 it is the portion employed in dna fingerprinting。 its practicality for this purposewas discovered accidentally by alec jeffreys； a scientist at the university of leicester in england。 in 1986jeffreys was studying dna sequences for genetic markers associated with heritable diseases when he wasapproached by the police and asked if he could help connect a suspect to two murders。 he realized his techniqueought to work perfectly for solving criminal cases…and so it proved。 a young baker with the improbable name ofcolin pitchfork was sentenced to two life terms in prison for the murders。
over 60 percent of human genes； it turns out； are fundamentally the same as those found infruit flies。 at least 90 percent correlate at some level to those found in mice。 （we even havethe same genes for making a tail； if only they would switch on。） in field after field；researchers found that whatever organism they were working on鈥攚hether nematode wormsor human beings鈥攖hey were often studying essentially the same genes。 life； it appeared； wasdrawn up from a single set of blueprints。
further probings revealed the existence of a clutch of master control genes； each directingthe development of a section of the body； which were dubbed homeotic （from a greek wordmeaning 鈥渟imilar鈥潱r hox genes。 hox genes answered the long…bewildering question of howbillions of embryonic cells； all arising from a single fertilized egg and carrying identicaldna； know where to go and what to do鈥攖hat this one should bee a liver cell； this one astretchy neuron； this one a bubble of blood； this one part of the shimmer on a beating wing。 itis the hox genes that instruct them； and they do it for all organisms in much the same way。
interestingly； the amount of genetic material and how it is organized doesn鈥檛 necessarily； oreven generally； reflect the level of sophistication of the creature that contains it。 we haveforty…six chromosomes； but some ferns have more than six hundred。 the lungfish； one of theleast evolved of all plex animals； has forty times as much dna as we have。 even themon newt is more genetically splendorous than we are； by a factor of five。
clearly it is not the number of genes you have； but what you do with them。 this is a verygood thing because the number of genes in humans has taken a big hit lately。 until recently itwas thought that humans had at least 100；000 genes； possibly a good many more； but thatnumber was drastically reduced by the first results of the human genome project； whichsuggested a figure more like 35；000 or 40；000 genes鈥攁bout the same number as are found ingrass。 that came as both a surprise and a disappointment。
it won鈥檛 have escaped your attention that genes have been monly implicated in anynumber of human frailties。 exultant scientists have at various times declared themselves tohave found the genes responsible for obesity； schizophrenia； homosexuality； criminality；violence； alcoholism； even shoplifting and homelessness。 perhaps the apogee （or nadir） of thisfaith in biodeterminism was a study published in the journal science in 1980 contending thatwomen are genetically inferior at mathematics。 in fact； we now know； almost nothing aboutyou is so acmodatingly simple。
this is clearly a pity in one important sense； for if you had individual genes that determinedheight or propensity to diabetes or to baldness or any other distinguishing trait； then it wouldbe easy鈥攑aratively easy anyway鈥攖o isolate and tinker with them。 unfortunately； thirty…five thousand genes functioning independently is not nearly enough to produce the kind ofphysical plexity that makes a satisfactory human being。 genes clearly therefore mustcooperate。 a few disorders鈥攈emophilia； parkinson鈥檚 disease； huntington鈥檚 disease； andcystic fibrosis； for example鈥攁re caused by lone dysfunctional genes； but as a rule disruptivegenes are weeded out by natural selection long before they can bee permanentlytroublesome to a species or population。 for the most part our fate and fort鈥攁nd even oureye color鈥攁re determined not by individual genes but by plexes of genes working inalliance。 that鈥檚 why it is so hard to work out how it all fits together and why we won鈥檛 beproducing designer babies anytime soon。
in fact； the more we have learned in recent years the more plicated matters have tendedto bee。 even thinking； it turns out； affects the ways genes work。 how fast a man鈥檚 beard grows； for instance； is partly a function of how much he thinks about sex （because thinkingabout sex produces a testosterone surge）。 in the early 1990s； scientists made an even moreprofound discovery when they found they could knock out supposedly vital genes fromembryonic mice； and the mice were not only often born healthy； but sometimes were actuallyfitter than their brothers and sisters who had not been tampered with。 when certain importantgenes were destroyed； it turned out； others were stepping in to fill the breach。 this wasexcellent news for us as organisms； but not so good for our understanding of how cells worksince it introduced an extra layer of plexity to something that we had barely begun tounderstand anyway。
it is largely because of these plicating factors that cracking the human genome becameseen almost at once as only a beginning。 the genome； as eric lander of mit has put it； is likea parts list for the human body： it tells us what we are made of； but says nothing about howwe work。 what鈥檚 needed now is the operating manual鈥攊nstructions for how to make it go。
we are not close to that point yet。
so now the quest is to crack the human proteome鈥攁 concept so novel that the termproteome didn鈥檛 even exist a decade ago。 the proteome is the library of information thatcreates proteins。 鈥渦nfortunately；鈥潯bserved scientific american in the spring of 2002； 鈥渢heproteome is much more plicated than the genome。鈥�
that鈥檚 putting it mildly。 proteins； you will remember； are the workhorses of all livingsystems； as many as a hundred million of them may be busy in any cell at any moment。 that鈥檚a lot of activity to try to figure out。 worse； proteins鈥櫋ehavior and functions are based notsimply on their chemistry； as with genes； but also on their shapes。 to function； a protein mustnot only have the necessary chemical ponents； properly assembled； but then must also befolded into an extremely specific shape。 鈥渇olding鈥潯s the term that鈥檚 used； but it鈥檚 amisleading one as it suggests a geometrical tidiness that doesn鈥檛 in fact apply。 proteins loopand coil and crinkle into shapes that are at once extravagant and plex。 they are more likefuriously mangled coat hangers than folded towels。
moreover； proteins are （if i may be permitted to use a handy archaism） the swingers of thebiological world。 depending on mood and metabolic circumstance； they will allowthemselves to be phosphorylated； glycosylated； acetylated； ubiquitinated； farneysylated；sulfated； and linked to glycophosphatidylinositol anchors； among rather a lot else。 often ittakes relatively little to get them going； it appears。 drink a glass of wine； as scientificamerican notes； and you materially alter the number and types of proteins at large in yoursy