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On The Gene: An Intimate History by Siddhartha Mukherjee. New York, NY: Scribner, 2016. 608 pages. $32.00.
“Three profoundly destabilizing scientific ideas ricochet though the 20th century . . . the atom, the byte, the gene.”
—Siddhartha Mukherjee
As a layman approaching the study of inheritance, I was disappointed to learn of DNA’s dull chemical code. The elixir of life was not earth, wind, fire and water but four nucleic acids named adenine, guanine, cytosine, and thymine (abbreviated AGCT). Now Siddhartha Mukherjee, a doctor and writer with a flair for metaphor, has written a book about the history of genetics that restores wonder to the creation story.
Aristotle thought the male semen delivered the plan and the female egg provided the material. Although wrong in thinking only the male contributed the plan, he understood that “heredity was transmission of a message.” Still for many years people believed a miniature person, called a homunculus, was curled up in the male sperm. As late as 1669 a Dutch scientist claimed, “Men come from small men as large trees from small cuttings.”
Darwin imagined that the cells of all organisms produce particles of information that were transmitted to sperm and egg, gemmules from the hand telling how to make a hand, gemmules from the ear, a new ear. He called this theory pangenesis, but accepted the criticism that the blending of male and female gemmules did not explain the variations needed for evolutionary theory.
Seven years after Darwin introduced The Origin of the Species in London, the German-speaking monk Gregor Mendel presented a paper on plant hybrids to a small group at the natural science society in Brno, which is now Czechoslovakia. His research was ignored until thirty years later when three scientists independently recognized what Mendel had discovered—that corpuscles of hereditary information moved from one generation to the next with hidden “submissive” traits showing up in future generations. The unit was named the gene and the idea took hold that “the unfurling of an embryo; the reach of a plant toward sunlight the ritual dance of bees—every biological activity required decoding of coded instructions.”
In 1944, Oswald Avery discovered DNA—the material substance of the gene that is in the nucleus of every cell. In 1953, guided by Rosalind Franklin’s X-ray photographs, Watson and Crick made their model of the double helix with its complementary bases (A attracted to G and T to C) linked together by a sugar phosphate backbone. Both strands contain the same information but each is a reflection or mirror image of the other. “The most appropriate analogy,” says Mukherjee, “is a yin yang structure.”
In 1958, John Gurdon, a scientist at Oxford, was able to clone tadpoles, using cells from the intestine of an adult frog. Mukherjee’s description of this experiment combines his detailed knowledge with his writing skill. Gurdon “used a beam of ultra violet light to lance the nucleus of an unfertilized egg. Then like a diver slicing the water, he punctured the egg membrane with a fire-shaped needle, barely riffling the surface, and blew in the nucleus.” “Bathed briefly in the elixir of egg cells, they became eighteen doppelgangers.”
In the winter of 2000 the complete human genome was sequenced. In his chapter called The Book of Man (in Twenty-Three Volumes), Mukherjee lists some of the findings:
Genes are arranged on chromosomes. We have 23 chromosomes, one less than apes that share 96 percent of our genomes The ends of chromosomes are marked by telomeres “like the bits of plastic at the end of shoe laces.”
Our DNA encodes more genes than flies and worms but less than rice or wheat. Number isn’t as important as gene regulation and gene splicing which is used more extensively in he human genome.
Enormous stretches of our DNA, 98 percent of the genome does not code for RNA. “If the genome were a lie stretching across the Atlantic Ocean between North America and Europe, genes would be occasional specks of land strewn across long, dark tracts of water.”
Fragments of DNA—some derived from ancient viruses—have been carried passively for millennia “like decommissioned traveling salesmen these pieces are permanently tethered to our genome.”
When I spoke to a young couple about this book, the man asked what is RNA, and I explained that RNA carries the DNA message to ribosomes, looms in the body of the cell that compose amino acids, leaving DNA safely in the nucleus. I see, said the woman, DNA is like a precious yeast starter kept at bakery headquarters.
Bread dough is expanded by yeast, a one-celled organism. Another one celled organism, a bacterium discovered by scientists in a Danish yogurt and cheese company, led Jennifer Doudna to use a protein in bacteria to make precise cuts in the genome. The food scientists had discovered that certain bacteria targeted viruses. “The war between viruses and bacteria,” says Mukherjee, “has gone on for so long and with such ferocity, that like ancient, conjoined enemies . . . their mutual animosity has been imprinted on their genes.” In 2012 Doudna isolated the protein in a bacterium that recognized and delivered the “lethal gash to the viral gene.” She then reprogrammed the protein to target specific defective genes. Doudna and other scientists have warned that gene editing should be used to eliminate hereditary diseases but not to “improve ourselves.”
Mukherjee speaks of Gregor Mendel’s tenderness, a word, he says, “that shares roots with tending—a gardener’s activity,” but also with “the stretching of a pea tendril toward the sunlight.” The author, a doctor, wrote of tending cancer patients in his first book The Emperor of All Maladies, and now as a research scientist, he gives attention—another word with the same root—to the code we share with all living cells, whether single or combined in plants and animals. “A gene from a blue whale,” he says, “can be inserted into microscopic bacterium and it will be deciphered accurately.”
Comments from other contributors to the Poetics of Science online discussion:
L. Shapley Bassen: Here, I feel, is a laudatory book review of the Mukherjee gene epic, celebrating its poetry. Interesting to read in context of Sara Talpos’s description of criticism re: the book/science writing. Calling the author “a Bard for the gene” was delightful. My favorite sentence was, “When I spoke to a young couple about this book, the man asked what is RNA, and I explained that RNA carries the DNA message to ribosomes, looms in the body of the cell that compose amino acids, leaving DNA safely in the nucleus. I see, said the woman, DNA is like a precious yeast starter kept at bakery headquarters.” But another sentence struck me more forcefully: “Our DNA encodes more genes than flies and worms but less than rice or wheat. Number isn’t as important as gene regulation and gene splicing which is used more extensively in the human genome.” That less metaphorical expression [double entendre!] is a bobbydazzler.