Meiosis and preimplantation genetic testing

This commentary was mainly written to clarify a fundamental concept related to meiosis, which is the type of cell division for the production of gametes. Meiosis consists of two nuclear and cell divisions without an intermediate phase, starting with a diploid cell while giving rise to four haploid cells. Each division (meiosis I and meiosis II) consists of four stages: a) prophase, b) metaphase, c) anaphase and d) telophase. Recently, we noticed that there is an error in some schematic diagrams depicting meiosis I. These diagrams connect oocytes and polar bodies in different ways. For example, in a recent article, we noticed that in both the text and the schematic diagram “primary oocyte” and “polar body I” and “secondary oocyte” and “polar body II” appear in parallel. However, this is incorrect. Actually, the secondary (not primary) oocyte corresponds to polar body I. This is a fundamental knowledge that is necessary to understand the whole miracle of meiosis and the steps of preimplantation genetic testing.