Final answer:
Breasts in females and deeper voices in males are secondary sex characteristics that develop during puberty, influenced by hormones such as estrogen and testosterone. Primary sex characteristics are those directly involved in reproduction, like ovaries in females and testes in males.
Step-by-step explanation:
The development of breasts in females and deeper voices in males are not examples of primary sex characteristics; rather, they are considered secondary sex characteristics. Primary sexual characteristics are those directly involved in reproduction, such as the uterus and ovaries in females and the testes in males. Secondary sexual characteristics, on the other hand, are features that develop during puberty but are not directly involved in reproduction. These include the development and maturation of breasts in females, which is mainly influenced by the estrogens, and the deepening of the voice in males, which is due to the elongation of the larynx and is influenced by testosterone levels. Other female secondary sex characteristics include the broadening of hips and growth of pubic hair, while male secondary characteristics include the growth of facial and pubic hair, as well as broadening of the shoulders.
During adolescence, the onset and pace of puberty and the development of these characteristics vary widely among individuals, but overall, the sequence of physical changes is predictable. Testosterone not only contributes to male secondary sex characteristics like a deepened voice but also stimulates spermatogenesis, while estrogen is responsible for the development of female secondary sex characteristics such as breast growth.