Polarkropp

Polarkropp, or polar body, is a small haploid cell produced during oogenesis as a byproduct of meiosis. It contains little cytoplasm and typically does not develop into a functioning gamete. The main role of polar bodies is to discard the extra sets of chromosomes produced during meiosis, allowing the oocyte to retain most of the cytoplasm needed for early embryo development.

Formation occurs during meiotic divisions in the developing egg cell. In meiosis I, the primary oocyte divides to form a large secondary oocyte and a small first polar body. The secondary oocyte then proceeds to meiosis II; in many species meiosis II is completed after fertilization, resulting in an ovum and a second polar body. The first polar body may sometimes divide again, producing up to three polar bodies in total. Polar bodies are generally nonfunctional and are typically degraded.

Polarkropp finnes hos mange dyr og spiller en rolle som et byrå for genetisk materiale i oogenesen. De har liten eller ingen rolle i fertilisering og embryo­utvikling, men de kan være gjenstand for studier i reproduktiv biologi og, i noen tilfeller, i preimplantatorisk genetisk testing ved analyse av mors genetiske materiale. I praksis er polar bodies ofte sett som biologiske biprodukter av meiosen.

Se også: meiosis, oogenese, fertilisering, gametogenese.