The combination of much higher levels of androgens (about 10-fold higher) and much lower levels of estrogen (about 10-fold less), due to the ovaries in females producing high amounts of estrogens but low amounts of androgens and the testes in males producing high amounts of androgens but low amounts of estrogens, are why males generally do not grow prominent or well-developed breasts relative to females.Calcitriol, the hormonally active form of vitamin D, acting through the vitamin D receptor (VDR), has, like the androgens, been reported to be a negative regulator of mammary gland development in mice, for instance, during puberty. VDR knockout mice show more extensive ductal development relative to wild-type mice, as well as precocious mammary gland development. In addition, VDR knockout has also been shown to result in increased responsiveness of mouse mammary gland tissue to estrogen and progesterone, which was represented by increased cell growth in response to these hormones. Conversely however, it has been found that VDR knockout mice show reduced ductal differentiation, represented by an increased number of undifferentiated TEBs, and this finding has been interpreted as indicating that vitamin D may be essential for lobuloalveolar development.
Hence, left-handed basketball players tend to use their right leg more as they finish a left handed layup (although both right- and left-handed players are usually able to use both hands when finishing near the basket). In the National Football League, a disproportionate, and increasing, number of punters punt with their left leg, where punting is the position in play that receives and kicks the ball once it leaves the line of scrimmage. At the end of the 2017 NFL season, 10 out of the leagues 32 punters were left-footed, up from four out of 31 (not counting dual-footed punter Chris Hanson, who left the league in 2009) at the beginning of the millennium; in contrast, placekickers were almost exclusively right-footed. The only apparent advantage to punting with the left foot is that, because it is not as common, return specialists are not as experienced handling the ball spinning in the opposite direction. Boardsports
In boardsports (e.g., surfing, skateboarding and snowboarding), one stands erect on a single, lightweight board that slides along the ground or on water. The need for balance causes one to position the body perpendicular to the direction of motion, with one foot leading the other. As with handedness, when this task is repetitively performed, one tends to naturally choose a particular foot for the leading position. Goofy stance vs. regular stance
Boardsport riders are "footed" in one of two stances, generally called "regular" and "goofy". Riders will generally quickly choose a preferred stance that becomes permanently preferred.