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3. Not so thrifty diabetes genes > Genetics of Obesity

Genetics of Obesity

Anyone in any doubt about the power of genes to influence weight gain need only consider the case of obese mutant mice. These are a strain of otherwise normal mice that appeared in a laboratory colony as a result of a spontaneous mutation in 1950. Animals that inherit two copies of the mutation are really big, up to four or five times bigger than littermates with just a single bad copy of the affected gene, big enough to swallow up their siblings in the flabby folds of their skin. They get this way because they are unable to control their appetite, and just keep eating.

In the mid-1990s it was discovered that the obese mutation knocks out a gene that encodes the peptide hormone leptin. Leptin is one of the primary signals that the brain uses to stop us eating when it senses that we’ve had enough. The crucial part of the brain is called the hypothalamus, which among other things is also known as the satiety center. In other words, we don’t just stop eating after a meal because there’s no more food on the plate, but rather because we have finely tuned sensors that actively tell us it is time to stop eating. Disrupt those sensors, and we keep eating, and obesity is sure to follow.


  

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