Mouse mutations can affect an animal's appetite and eating habits. The ob gene produces a satiety factor (the hormone leptin). The db gene product is required to respond to the satiety factor (the leptin receptor). Leptin is a product of adipose cells. Therefore, a very obese mouse would be expected to have which of the following? A. increased gene expression of ob and decreased expression of db B. increased gene expression of db and decreased expression of ob C. decreased transcription of both ob and db D. mutation of ob or db