Obesity could be inherited in more ways according to the phenotypes of the gene. This genes maybe mutilated over time and eventually that will be triggered if you are adopting certain food habits. This inheritable obesity stays dormant when you don’t provide a way to make it work. It’s same like height factor also, you got a major chance to get the height as inheritable fact if you push it forward. For reference, height is estimated heritabilities of 0.6-0.8
Leptin is unlikely to be the main factor, and the figure of 5-10 lbs does not make any sense. Experimental mutations in the leptin gene in mice do induce obesity, but in humans the panorama is not clear: the common polymorphisms in the leptin gene do not clearly associated with obesity, because there are huge environmental factors involved, some of which can involve the leptin gene itself. Apparently a diet rich in fructose in infancy leads to a deceased leptin level, for example. Leptin is the “satiety” hormone so this could induce weight gain. Interestingly, obese people have higher levels of leptin than non obese people, mainly because they have increased body fat, and leptin is expressed in fat, and they do not respond to leptin as non obese people do, which is to feel full and stop eating.
Genetics of obesity is under heavy research study, and the genetic link has been discovered. There are over 100 regions on the human genome that are responsible for the development of obesity. In mice researchers have shown that turning off one particular gene which encodes a protein called 14-3-3zeta, found in every cell in the body, results in a 50% reduction of white fat in mice, even when the mice ate the same food.
But it only means that one is genetically predisposed to the condition. It requires a trigger. A parent who feeds her children properly, encourages exercise, provides lots of love, and takes her child to a pediatrican regularly is less likely to trigger the Obesity gene than a parent who feeds her child garbage, allows the child to watch TV and play on the computer all day, and provides little love (or is neglectful or abusive).