Homie, there’s so much confusion is such a small space…
Yes, it’s genetic. Biological sex is determined by genes in humans. No, it’s not epigenetic. That refers to how environmental conditions influence the expression of your genetic inventory. The male sex chromosome is about 70% the size of the female one; males lack it entirely, it’s not present but being suppressed by methylation.
It is not dominance in the relevant sense of the word. It is true, however, than biological sex is entirely determined by the male gamete — the sperm. The ovum always carries an X, each sperm contains either an X or a Y.
Compared to most other animals, mammals have one of the simplest sex determination systems around.