Final answer:
Testosterone is the hormone that most influences sex in embryonic development. It is produced following stimulation by the SRY gene on the Y chromosome and is responsible for the development of male reproductive organs. Without the SRY gene or adequate testosterone, embryonic development will result in female reproductive organs.
Step-by-step explanation:
The hormone that most influences sex in embryonic development is testosterone. This hormone is pivotal in the differentiation and development of the male reproductive system. During the initial weeks of embryonic development, the SRY gene on the Y chromosome stimulates the production of proteins that induce the formation of testes from undifferentiated gonadal tissue. The testes, in turn, secrete testosterone, which leads to the development of male sexual organs. In the absence of the Y chromosome, and thus the absence of the SRY gene, an embryo will naturally develop into female, as the default reproductive system is female; characterized by the production of estrogen and the development of ovaries and female reproductive organs.
It is important to note that abnormalities in the SRY gene can lead to conditions such as Swyer syndrome, where an embryo with a typical male XY chromosome pattern does not develop male characteristics due to SRY gene malfunction. In the absence of sufficient testosterone or functional SRY expression on the Y chromosome, the embryo will develop female sex characteristics regardless of the chromosomal composition.