Polar body
Polar bodies , also called polar bodies or directional bodies , are formed in the course of maturation or reduction division ( meiosis ) and adhere to the (future) egg cell . In many species, the polar bodies determine the animal pole of the egg cell, but not so in humans.
They are haploid , relatively poor in cytoplasm and are usually broken down (degenerate).
In humans (as in all vertebrates) there are two kinds of polar bodies. The first is formed during meiosis in the first meiosis of the primary oocyte and has a haploid chromosome set with 23 2-chromatid chromosomes . The secondary oocyte is formed when it divides. In the second meiotic division, the secondary oocyte is divided into another polar body and the mature egg cell. The polar body, which arose during the first meiosis, can also divide; So there are up to three polar bodies in the end.
The polar body can during the polar body , a possible type of preconception or preimplantation genetic diagnosis , to study the female germline genetic peculiarities before the implantation of in vitro fertilized ( " in vitro fertilization ") embryos are used.
literature
- Rene Fester Kratz, Donna Rae Siegfried, Kathrin Friederike Stock: Biology for Dummies . John Wiley & Sons, 2011, ISBN 978-3-527-70738-6 , p. 350.
Individual evidence
- ^ Campbell, Neil A. / Reece Jane B .: Biology. 6th edition, Pearson 2006, p. 1181
- ↑ University of Bern: The penetration of the spermatozoon into the oocyte , accessed on October 1, 2015