Molecular_Hubbard%20and%20Wald,%201997

Molecular_Hubbard%20and%20Wald,%201997 - ~,~"~ E XPLODING T...

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r ~--"-,~--""~."' EXPLODING THE GENE MYTH Harry Laughlin of the Eugenics Record Office was one of the most important lobbyists and witnesses in favor of the Immigration Restric- tion Act at the congressional hearings that preceded its passage and was dignified with the title of "expert eugenical agent" by the House Com- mittee on Immigration and Naturalization. THREE . . . . . . . . . . . . . . .. . . . . . .. .. . . . . .. . . . . . . THE NEW EUGENICS: TESTING, SCREENING, AND CHOICE OVERT AND SUBTLE EUGENICS Interest in eugenics declined after the Second World War. Traditional co- lonialism was in retreat and the United Nations held out the hope of a future in which the peoples of the world could meet on an equal basis. Revulsion against Nazi eugenic practices led to a reaction against the whole idea of "better" and "worse" races. While racism did not disap- pear, people couched their racist attacks in different language, speaking of their targets as "underdeveloped," rather than genetically inferior. The suggestion was that we are all human, though some of us may be more culturally or socially advanced. As eugenics became politically unacceptable, within the scientific community it was also losing favor for pragmatic reasons. Scientists be- gan to realize that most inherited conditions are recessive, rather than dominant. Someone with a dominant genetic condition will pass it on to roughly half of her or his descendants. But to inherit a recessive condi- tion, people must receive copies of the relevant allele, or form of the gene, from both their parents. If they inherit only one copy from one parent, they generally show no symptoms and are said to be carriers for that condition. Even if two carriers have children together, each child has only one chance in four of manifesting the condition. Familiar examples of recessive conditions are phenylketonuria, or PKU (a metabolic problem that can result in mental retardation), cystic fibrosis (a glandular disturbance that leads to the accumulation of mucus in the lungs and to repeated infections), Tay Sachs disease (a fatal neurological disease of young children), and sickle-cell anemia (a blood disease that can be extremely painful and disabling). Because these conditions are recessive, people who manifest them 23 22
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<~-.---~.- -.-.--~"------~--.~ EXPLODING THE GENE MYTH (those with two copies of the affected allele) are only a fraction of those who carry at least one copy. This is because most alleles associated with recessive conditions are carried by people who have no symptoms and often have no reason to suspect that they are carriers. Recessive muta- tions are propagated by healthy, "normal" members of the population. Early in this century, the British mathematician G. H. Hardy and the German physician W. Weinberg, working independently, developed a mathematical theorem for calculating the number of carriers for a reces- sive condition in a population by looking at the number of people who manifest the condition. For example, one in 25,000 people in the United States has PKU (that is, two copies of the relevant allele). Using the Hardy-Weinberg theorem, one can calculate from this that
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