eli5 if testosterone is produced in the testes and estrogen in the ovaries,how do females have small amounts of testosterone and males have small amounts of estrogen in their bodies?
Women actually have more testosterone than estrogen, usually.
It’s just that men have a _lot_ more testosterone than women do.
Every cell in a human body has the same DNA and therefore the same complement of genes. Every gene encodes a single kind of protein. These proteins serve as catalysts for chemical reactions that turn some substances in the body into other substances, including the reactions that turn cholesterol into testosterone, or cholesterol into estradiol etc. So human sex hormones can actually be produced in a lot of different places and regardless of the sex of the individual, since everyone is equipped with all the necessary things for it on the cellular level. Testes and ovaries are just the specialized places which tend produce a lot of the corresponding hormones.