Simple observation suggests overweight and obesity tend to run in families. The search for genes that affect the tendency to pack on pounds has found a growing list of genes that each contribute to overall risk. The most famous of these genes is the FTO gene on chromosome 16 - the presence of specific "risky" versions of this gene is correlated with an extra 3 pounds for each risk-increasing copy (we have 2 copies of each gene).
But overweight and obesity are clearly influenced only partly by genetics and we can also explain the tendency for familial overweight by the fact that families often share eating and activity habits.
It's also clear that during the past three decades, while obesity rates have tripled, the genetic makeup of the population has not changed dramatically. Therefore environmental factors (food intake and activity levels) are clearly responsible for this rapid rise in obesity. The genetic makeup can only take responsibility for making some people moreRead More »from Can a genetic test tell if you’re going to gain weight?