The Gene: An Intimate History - Siddhartha Mukherjee Page 0,6

is identified as the source of genetic information. The “action” of a gene is described in mechanistic terms: genes encode chemical messages to build proteins that ultimately enable form and function. James Watson, Francis Crick, Maurice Wilkins, and Rosalind Franklin solve the three-dimensional structure of DNA, producing the iconic image of the double helix. The three-letter genetic code is deciphered.

Two technologies transform genetics in the 1970s: gene sequencing and gene cloning—the “reading” and “writing” of genes (the phrase gene cloning encompasses the gamut of techniques used to extract genes from organisms, manipulate them in test tubes, create gene hybrids, and produce millions of copies of such hybrids in living cells.) In the 1980s, human geneticists begin to use these techniques to map and identify genes linked to diseases, such as Huntington’s disease and cystic fibrosis. The identification of these disease-linked genes augurs a new era of genetic management, enabling parents to screen fetuses, and potentially abort them if they carry deleterious mutations (any person who has tested their unborn child for Down syndrome, cystic fibrosis, or Tay-Sachs disease, or has been tested herself for, say, BRCA1 or BRCA2 has already entered this era of genetic diagnosis, management, and optimization. This is not a story of our distant future; it is already embedded in our present).

Multiple genetic mutations are identified in human cancers, leading to a deeper genetic understanding of that disease. These efforts reach their crescendo in the Human Genome Project, an international project to map and sequence the entire human genome. The draft sequence of the human genome is published in 2001. The genome project, in turn, inspires attempts to understand human variation and “normal” behavior in terms of genes.

The gene, meanwhile, invades discourses concerning race, racial discrimination, and “racial intelligence,” and provides startling answers to some of the most potent questions coursing through our political and cultural realms. It reorganizes our understanding of sexuality, identity, and choice, thus piercing the center of some of the most urgent questions coursing through our personal realms.III

There are stories within each of these stories, but this book is also a very personal story—an intimate history. The weight of heredity is not an abstraction for me. Rajesh and Jagu are dead. Moni is confined to a mental institution in Calcutta. But their lives and deaths have had a greater impact on my thinking as a scientist, scholar, historian, physician, son, and father than I could possibly have envisioned. Scarcely a day passes in my adult life when I do not think about inheritance and family.

Most important, I owe a debt to my grandmother. She did not—she could not—outlive the grief of her inheritance, but she embraced and defended the most fragile of her children from the will of the strong. She weathered the buffets of history with resilience—but she weathered the buffets of heredity with something more than resilience: a grace that we, as her descendants, can only hope to emulate. It is to her that this book is dedicated.

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I. By byte I am referring to a rather complex idea—not only to the familiar byte of computer architecture, but also to a more general and mysterious notion that all complex information in the natural world can be described or encoded as a summation of discrete parts, containing no more than an “on” and “off” state. A more thorough description of this idea, and its impact on natural sciences and philosophy, might be found in Information: A History, a Theory, a Flood by James Gleick. This theory was most evocatively proposed by the physicist John Wheeler in the 1990s: “Every particle, every field of force, even the space-time continuum itself—derives its function, its meaning, its very existence entirely . . . from answers to yes-or-no questions, binary choices, bits . . . ; in short, that all things physical are information-theoretic in origin.” The byte or bit is a man-made invention, but the theory of digitized information that underlies it is a beautiful natural law.

II. In certain bacteria, chromosomes can be circular.

III. Some topics, such as genetically modified organisms (GMOs), the future of gene patents, the use of genes for drug discovery or biosynthesis, and the creation of new genetic species merit books in their own right, and lie outside the purview of this volume.

PART ONE

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THE “MISSING SCIENCE OF HEREDITY”

The Discovery and Rediscovery of Genes

(1865–1935)

This missing science of heredity, this unworked mine of knowledge on the borderland of biology and anthropology, which for all practical purposes is as unworked now