Reduced penetrance and variable expressivity are factors that influence the effects of particular genetic changes. These factors usually affect disorders that have an autosomal dominant pattern of inheritance, although they are occasionally seen in disorders with an autosomal recessive inheritance pattern.enetrance refers to the proportion of people with a particular genetic change (such as a mutation in a specific gene) who exhibit signs and symptoms of a genetic disorder. If some people with the mutation do not develop features of the disorder, the condition is said to have reduced (or incomplete) penetrance.
Although men have more muscle mass than women, both sexes reach their physical peak as young adults or anywhere from their late 20's to early 30's, according to âHuman Development: A Life-Span Viewâ by Robert Kail and John Cavanaugh.
1 Boys enter puberty about one year later than girls. 2  The first sign is enlargeÂ­ment of the testes and a thinning and reddening of the scrotum, which hapÂ­pens at an average age of eleven but may occur anytime between nine to fourteen years. For boys, the peak growth period occurs about two years after the beginning of puberty. 2  If a boy shows no signs of puberty by age 14, consult with your pediatrician. 3  See Physical Development in Boys: What to Expect.