Final Answer:
The primary sex characteristics develop as the fetus is growing in the womb, when the chromosomes of the 23rd pair cause the release of the proper hormones to stimulate the growth of the sex organs. Thus, the correct answer is D. the fetus is growing in the womb, when the chromosomes of the 23rd pair cause the release of the proper hormones to stimulate the growth of the sex organs.
Step-by-step explanation:
The development of primary sex characteristics occurs due to the genetic influence of the sex chromosomes during fetal growth. Chromosomes from the 23rd pair determine an individual's biological sex, leading to the release of specific hormones that dictate the development of sex organs.
In embryos with XX chromosomes, ovaries develop due to the presence of estrogen, while in embryos with XY chromosomes, testes form under the influence of testosterone.
The fetal gonads, influenced by the sex chromosomes, produce hormones that trigger the development of either male or female reproductive organs. This process occurs independently of external behavioral cues or postnatal environmental factors. As the fetus grows, the genetic information directs the intricate cascade of hormonal signals, initiating the differentiation and development of the reproductive system.
Behavioral cues, upbringing, or milk components do not directly impact the development of primary sex characteristics. Instead, it's the orchestrated interplay of genetic instructions, particularly the sex chromosomes, that orchestrates the release of appropriate hormones, which in turn guide the formation of the reproductive organs during fetal development. Hence, the primary sex characteristics are primarily determined by genetic factors and hormonal influences in the womb.
Thus, the correct answer is D. the fetus is growing in the womb, when the chromosomes of the 23rd pair cause the release of the proper hormones to stimulate the growth of the sex organs.