London: Researchers have discovered a single gene, which may have a measurable impact on a person’s brain size as well as intelligence.There is little debate about genetics being behind considerable variation in people’s intelligence, but studies have constantly failed to zero in on any single gene that has a significant impact. Instead, researchers usually find that hundreds of genes contribute.A large-scale genetics study depending on fMRI brain scans and DNA samples from more than 20,000 people has revealed what is claimed as the biggest effect yet of a single gene on intelligence – although the effect is small as the gene alters IQ by only 1.29 points.According to some researchers, that basically proves that intelligence depends on the action of a number of genes after all.“It seems like the biggest single-gene impact we know of that affects IQ,” the New Scientist quoted Paul Thompson of the University of California, Los Angeles, who led the collaboration of 207 researchers as saying.“But it`s not a massive effect on IQ overall,” he said.The variant is in a gene called HMGA2, which has earlier been tied to people’s height. At the site of the relevant mutation, the IQ difference relies on a change of a single DNA “letter” from C, standing for cytosine, to T, standing for thymine.“C is the good one,” said Thompson.Apart from raising IQ by 1.29, it boosts the overall volume of the brain – but only by 0.58 per cent of average brain size, adding around 9 cubic centimetres of tissue.“It’s a loss or gain of about 2 teaspoons,” insisted Thompson.The brain-size-altering effect of the gene is what guided the researchers to evaluate the impact on IQ.
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