During which stage of meiosis does the process begin in utero?

The process of meiosis begins in utero during prophase of meiosis I. In the developing female fetus, primordial germ cells migrate to the developing ovaries and undergo mitotic divisions to form oogonia. Around the time of birth, these oogonia enter prophase I of meiosis and become primary oocytes, which remain arrested in this stage until puberty.

During prophase I, there are several critical processes that take place, including the pairing of homologous chromosomes, crossing over (exchange of genetic material between homologs), and the formation of tetrads. This prepares the oocytes for subsequent stages of meiosis, although they will not complete the first meiotic division until ovulation occurs later in life.

By focusing on prophase of meiosis I, one understands that it's not just the initiation of meiotic division, but the beginning of important genetic processes that will influence genetic diversity in future generations.