So, we know that typically, in order for a genetically diverse organism to be created, it must receive a merge of parent DNA. Now, we also know that in order for the daughter cell to have a proper number of chromosomes (Example, 46 in Homo Sapiens), the two contributing parents must both provide fertilization gametes with half the number of chromosomes that would normally be found in the somatic cells of the given species (So in Homo Sapiens, the chromosomal gamete number would be 23). So, as we know, the process which is undergone in the reproductive system to produce these haploid cells, is called Meiosis, and consists of two stages. Now here is where the complication comes in; for males, Meiosis I (Which produces two haploid cells [with duplicated chromosomes] from one reproductive cell) and Meiosis II (Which produces four haploid gametes [with unduplicated chromosomes] from the two haploid cells) happen consecutively, in the process known as Spermatogenesis, and produce four haploid gametes from a single reproductive cell. However, in females, who undergo Oogenesis, the process differs, as after Meiosis I (Which results in only one haploid cell [with duplicated chromosomes], and one Useless Polar Body, due to uneven cytoplasm distribution during cytokineses), the process pauses, and only continues with Meiosis II upon fertilization. Now my question is, why does Meiosis II only resume upon fertilization? Why can't Meiosis II just occur beforehand, producing one polar body and one potential egg cell [with unduplicated chromosomes], which would then be fertilized? Is there some sort of cytostatic agent that is depleted upon contact with sperm proteins?