9:3:3:1 would be the expected phenotypic ratio
Gynecomastia is an increase in the size of the mammary gland in men. The condition can occur in one or both breasts. It starts as a small mass under the nipple, which can be sensitive. One breast can be bigger than the other. Its cause is an imbalance between the stimulatory effects of estrogen (female sex hormones) and the inhibitory effects of androgens (male sex hormones) in the breast tissue, when the first ones increase, or the second ones descend.
Gynecomastia is a problem relatively common in the population, and there are three prevalence peaks throughout life:
Newborns: Between 60 and 90% of newborns have gynecomastia, produced by the passage of maternal estrogens through the placenta. It is a transient gynecomastia that disappears in about 2-3 weeks.
Puberty: Gynecomastia in puberty affects mainly young people aged between 10 and 14 years, and is due to the transient and physiological increase in estrogen that occurs at this age.
Elderly: Is due to an increase in fatty tissue with a greater peripheral aromatization ( a process that occurs in adipose tissue and that involves the conversion of androgens into estrogens), a decrease in the production of testosterone by the testes and the use of drugs.
The three examples of stimulus include;
1. Hit the skin with a needle or pin is a good example of stimulus. The sudden removing of the hand is the response.
2. When somebody bangs a door you jump if you were unaware because of the sound. The jumping is the response to a stimulus.
3. Holding a hot plate we fling hand away from it. The stimulus here is holding the plate while removal of the hand is the response.
Stimulus is the change or cause in an organism's surrounding which causes the organisms to react.
They provide an important habitat!
