The Gene, An Intimate History

Od tohto pána som pred dvoma rokmi čítala “životopis” rakoviny – knižku Emperor of all maladies. Natoľko sa mi páčila, že keď som zistila, že napísal ďlašiu knihu, tak som ju tiež kúpila. A nesklamal. Táto kniha je o génoch, o tom, čo si ľudia o nich kedysi mysleli, čo a ako sa o nich dodnes zistilo, filozofovanie o tom, prečo je to jeden z najnebezpečnejších a zároveň najúžasnejších objavov a nakuknutie do možnej budúcnosti. 

Pár úryvkov na zamyslenie a na namotanie sa:

Consider the genesis of a single-celled embryo produced by the fertilization of an egg by a sperm. The genetic material of this embryo comes from two sources: paternal genes (from sperm) and maternal genes (from eggs). But the cellular material of the embryo comes exclusively from the egg; the sperm is no more than a glorified delivery vehicle for male DNA—a genome equipped with a hyperactive tail. Aside from proteins, ribosomes, nutrients, and membranes, the egg also supplies the embryo with specialized structures called mitochondria. These mitochondria are the energy-producing factories of the cell; they are so anatomically discrete and so specialized in their function that cell biologists call them “organelles”—i.e., mini-organs resident within cells. Mitochondria, recall, carry a small, independent genome that resides within the mitochondrion itself—not in the cell’s nucleus, where the twenty-three pairs of chromosomes (and the 21,000-odd human genes) can be found. The exclusively female origin of all the mitochondria in an embryo has an important consequence. All humans—male or female—must have inherited their mitochondria from their mothers, who inherited their mitochondria from their mothers, and so forth, in an unbroken line of female ancestry stretching indefinitely into the past. (A woman also carries the mitochondrial genomes of all her future descendants in her cells; ironically, if there is such a thing as a “homunculus,” then it is exclusively female in origin—technically, a “femunculus”?) Now imagine an ancient tribe of two hundred women, each of whom bears one child. If the child happens to be a daughter, the woman dutifully passes her mitochondria to the next generation, and, through her daughter’s daughter, to a third generation. But if she has only a son and no daughter, the woman’s mitochondrial lineage wanders into a genetic blind alley and becomes extinct (since sperm do not pass their mitochondria to the embryo, sons cannot pass their mitochondrial genomes to their children). Over the course of the tribe’s evolution, tens of thousands of such mitochondrial lineages will land on lineal dead ends by chance, and be snuffed out. And here is the crux: if the founding population of a species is small enough, and if enough time has passed, the number of surviving maternal lineages will keep shrinking, and shrinking further, until only a few are left. If half of the two hundred women in our tribe have sons, and only sons, then one hundred mitochondrial lineages will dash against the glass pane of male-only heredity and vanish in the next generation. Another half will dead-end into male children in the second generation, and so forth. By the end of several generations, all the descendants of the tribe, male or female, might track their mitochondrial ancestry to just a few women. For modern humans, that number has reached one: each of us can trace our mitochondrial lineage to a single human female who existed in Africa about two hundred thousand years ago. She is the common mother of our species. We do not know what she looked like, although her closest modern-day relatives are women of the San tribe from Botswana or Namibia. I find the idea of such a founding mother endlessly mesmerizing. In human genetics, she is known by a beautiful name — Mitochondrial Eve.

… the largest “negative eugenics” project in human history was not the systemic extermination of Jews in Nazi Germany or Austria in the 1930s. That ghastly distinction falls on India and China, where more than 10 million female children are missing from adulthood because of infanticide, abortion, and neglect of female children.

McKusick’s belief in this paradigm – the focus on disability rather than abnormalcy – was actualized in the treatment of patients in his clinic. Patients with dwarfism, for instance, were treated by an interdisciplinary team of genetic counselors, neurologists, orthopedic surgeons, nurses, and psychiatrists trained to focus on specific disabilities of persons with short stature. Surgical interventions were reserved to correct specific deformities as they arose. The goal was not to restore “normalcy” – but vitality, joy, and function. […] And here too “fitness” could not be judged in absolutes. Rather the lack of fitness – illness in colloquial terms – was defined by the relative mismatch between an organism and environment.

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