We are interested in factors that contribute to obesity. The
discovery of the hormone leptin suggests that appetite control is
influenced by this compound. Biologists have identified a strain of
mutant mice that become obese when offered free access to food.
However, genetic analysis shows that this particular strain of mice
are "wild-type" (ob+) for the leptin gene, and do produce the
compound. Based on the parabiosis experiments in mice that we
reviewed, explain what might be causing these mice...