单选题 In the angry debate over how much of IQ comes from the genes that children inherit from parents and how much comes from experiences, one little fact gets overlooked: no one has identified any genes (other than those that cause retardation) that affect intelligence. So researchers led by Robert Plomin of London's Institute of Psychiatry decided to look for some:
Plomin's colleagues drew blood from two groups of 51 children each. They are all White living in six counties around Cleveland. In one group, the average IQ is 136. In the other group, the average IQ is 103. Isolating the blood cells, the researchers then examined each child's chromosome 6 (One of the 23 human chromosomes). Of the 37 land marks on chromosome 6that the researchers looked for, one jumped out: a form of gene called IGF2R occurred in twice as many children in high IQ group as in the average grouw-32 percent versus 16 percent. The study concludes that it is this form of the IGF2R gene, called allele 5, that contributes to intelligence.
Plomin cautions that "This is not a genius gene. It is one of many." (About half the differences in intelligence between one person and another are thought to reflect different genes, and half reflect different life experiences.)The gene accounts for no more than four extra IQ points. And it is neither necessary nor sufficient for high IQ: 23 percent of the average-IQ kids did have it, but 54 percent of genius kids did not.
The smart gene is known by the snappy name "insulin like growth factor 2 receptor" (IGH2R to its fun). It lets hormones like one similar to insulin dock with cells. Although a gene involved with insulin is not the most obvious candidate for an IQ gene, new evidence suggests it might indeed play the role. Sometimes when s hormone docks with the cell, it makes the cell grow; sometimes it makes the cell commit suicide. Both responses could choreograph the development of the brain. Scientists at the National Institutes of Health find that insulin can stimulate nerves to grow. And in rat brains, regions involved in learning and memory are chock full of insulin receptors.
Even though this supports the idea that IGF2R can affect the brain and hence intelligence, some geneticists see major problems with the IQ-gene study. One is the possibility that Plomin's group fell for what's called the chopsticks fallacy. Geneticists might think they've found a gene for chopsticks dexterity, but all they've really found is a gene more common in Asians than, say, Africans. Similarly, Plomin's IQ gene might simply be one that is more common in groups that emphasize academic achievement. "What if the gene they've found reflects ethnicity?" asks geneticist Andrew Feinberg of Johns Hopkins University. "I would take these findings with a whole box of salt./

单选题 As for how much of IQ comes from the genes and how much come from experiences,______.

单选题 A healthy person has______. chromosomes all together.

单选题 It is found that insulin______.

单选题 Some geneticists don't accept the IGF2R gene-study because______.

单选题 The phrase "with a whole box of salt" in the last paragraph means______.