When does genetic sex determination occur in a person and what is the reason for this?

This happens at the time of fertilization. As you know, the female reproductive cell carries in itself, in addition to 22 chromosomes, another X – chromosome, and the spermatozoon also contains, in addition to 22 chromosomes, the twenty-third either X or Y – chromosome. Which sperm will fertilize the egg, the person will have that sex. If a sperm with an X chromosome fertilizes, then there will be a female organism, and if a sperm with a Y chromosome, then there will be a male organism. The likelihood of a male or female body is about the same, but slightly more boys are born than girls. In different countries, the preponderance is from one hundred and four to one hundred and seven boys per hundred girls born.