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lly through the pus in surgicalbandages； miescher found a substance he didn’t recognize and called it nuclein （because itresided in the nuclei of cells）。 at the time； miescher did little more than note its existence； butnuclein clearly remained on his mind； for twenty…three years later in a letter to his uncle heraised the possibility that such molecules could be the agents behind heredity。 this was anextraordinary insight； but one so far in advance of the day’s scientific requirements that itattracted no attention at all。
for most of the next half century the mon assumption was that the material—nowcalled deoxyribonucleic acid； or dna—had at most a subsidiary role in matters of heredity。 itwas too simple。 it had just four basic ponents； called nucleotides； which was like having an alphabet of just four letters。 how could you possibly write the story of life with such arudimentary alphabet？ （the answer is that you do it in much the way that you create plexmessages with the simple dots and dashes of morse code—by bining them。） dna didn’tdo anything at all； as far as anyone could tell。 it just sat there in the nucleus； possibly bindingthe chromosome in some way or adding a splash of acidity on mand or fulfilling someother trivial task that no one had yet thought of。 the necessary plexity； it was thought；had to exist in proteins in the nucleus。
there were； however； two problems with dismissing dna。 first； there was so much of it：
two yards in nearly every nucleus； so clearly the cells esteemed it in some important way。 ontop of this； it kept turning up； like the suspect in a murder mystery； in experiments。 in twostudies in particular； one involving the pneumonococcus bacterium and another involvingbacteriophages （viruses that infect bacteria）； dna betrayed an importance that could only beexplained if its role were more central than prevailing thought allowed。 the evidencesuggested that dna was somehow involved in the making of proteins； a process vital to life；yet it was also clear that proteins were being made outside the nucleus； well away from thedna that was supposedly directing their assembly。
no one could understand how dna could possibly be getting messages to the proteins。 theanswer； we now know； was rna； or ribonucleic acid； which acts as an interpreter betweenthe two。 it is a notable oddity of biology that dna and proteins don’t speak the samelanguage。 for almost four billion years they have been the living world’s great double act； andyet they answer to mutually inpatible codes； as if one spoke spanish and the other hindi。
to municate they need a mediator in the form of rna。 working with a kind of chemicalclerk called a ribosome； rna translates information from a cell’s dna into terms proteinscan understand and act upon。
however； by the early 1900s； where we resume our story； we were still a very long wayfrom understanding that； or indeed almost anything else to do with the confused business ofheredity。
clearly there was a need for some inspired and clever experimentation； and happily the ageproduced a young person with the diligence and aptitude to undertake it。 his name wasthomas hunt morgan； and in 1904； just four years after the timely rediscovery of mendel’sexperiments with pea plants and still almost a decade before gene would even bee a word；he began to do remarkably dedicated things with chromosomes。
chromosomes had been discovered by chance in 1888 and were so called because theyreadily absorbed dye and thus were easy to see under the microscope。 by the turn of thetwentieth century it was strongly suspected that they were involved in the passing on of traits；but no one knew how； or even really whether； they did this。
morgan chose as his subject of study a tiny； delicate fly formally called drosophilamelanogaster； but more monly known as the fruit fly （or vinegar fly； banana fly； orgarbage fly）。 drosophila is familiar to most of us as that frail； colorless insect that seems tohave a pulsive urge to drown in our drinks。 as laboratory specimens fruit flies had certainvery attractive advantages： they cost almost nothing to house and feed； could be bred by themillions in milk bottles； went from egg to productive parenthood in ten days or less； and hadjust four chromosomes； which kept things conveniently simple。
working out of a small lab （which became known inevitably as the fly room） inschermerhorn hall at columbia university in new york； morgan and his team embarked ona program of meticulous breeding and crossbreeding involving millions of flies （onebiographer says billions； though that is probably an exaggeration）； each of which had to becaptured with tweezers and examined under a jeweler’s glass for any tiny variations ininheritance。 for six years they tried to produce mutations by any means they could think of—zapping the flies with radiation and x…rays； rearing them in bright light and darkness； bakingthem gently in ovens； spinning them crazily in centrifuges—but nothing worked。 morgan wason the brink of giving up when there occurred a sudden and repeatable mutation—a fly thathad white eyes rather than the usual red ones。 with this breakthrough； morgan and hisassistants were able to generate useful deformities； allowing them to track a trait throughsuccessive generations。 by such means they could work out the correlations betweenparticular characteristics and individual chromosomes； eventually proving to more or lesseveryone’s satisfaction that chromosomes were at the heart of inheritance。
the problem； however； remained the next level of biological intricacy： the enigmatic genesand the dna that posed them。 these were much trickier to isolate and understand。 aslate as 1933； when morgan was awarded a nobel prize for his work； many researchers stillweren’t convinced that genes even existed。 as morgan noted at the time； there was noconsensus “as to what the genes are—whether they are real or purely fictitious。” it may seemsurprising that scientists could struggle to accept the physical reality of something sofundamental to cellular activity； but as wallace； king； and sanders point out in biology： thescience of life （that rarest thing： a readable college text）； w