Quick Facts
Polar bodies are small nonfunctional cells with a haploid chromosome complement, consisting of a small amount of cytoplasm and a nucleus, resulting from unequal division of the primary oocyte(first polar body) and, if fertilization occurs, of the secondary oocyte(second polar body) (Dorland, 2011).
Related parts of the anatomy
Structure
The first polar body forms at the completion of the first meiotic division of the primary oocyte. The diploid (contains 46 chromosomes) primary oocyte completes meiosis I the day before ovulation, which results in the production of two haploid daughter cells (containing 23 chromosomes). These daughter cells are the secondary oocyte and the first polar body, both of which have identical chromosomal content.
The secondary oocyte and the first polar body differ in size as a result of the uneven manner in which the cytoplasm is shared between the two cells. The secondary oocyte is estimated to be 100 times larger in size that the first polar body. The first polar body, under normal circumstances, does not proceed to meiosis II with the secondary oocyte (Gitlin, Gibbons and Gosden, 2003; Meneely et al., 2017).
The polar body possesses a nucleus, ribosomes, Golgi apparatus, mitochondria, and cortical granules, and a number of additional cytoplasmic material, all with an uncertain level of functionality. The first polar body usually disintegrates by way of apoptosis within 24 hours.
The secondary oocyte commences meiosis II, which is arrested at metaphase until fertilization occurs.
Key Features/Anatomical Relations
The first polar body is located between the zona pellucida and the cell membrane of the secondary oocyte. The name “polar body” was coined from its polar position in the oocyte (Schmerler and Wessel, 2011).
Function
The function of the first polar body is to rid the secondary oocyte of the extra haploid set of chromosomes after meiosis I is completed.
The first polar body is useful in the process of artificial reproductive techniques. For instance, the structural assessment of the first polar body is used to assess fertilization, development, and implantation/pregnancy outcomes following in-vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI) (Gitlin, Gibbons and Gosden, 2003).
Polar bodies may also play a vital role in the evaluation of human genetic diseases. The genetic material situated within polar bodies can be used to ascertain the quality of an oocyte, as well as identify genetic aberrations in a minimally invasive assay (Schmerler and Wessel, 2011). Genetic analysis of the first polar body can be useful in screening for single gene defects in maternal mutations (Strauss and Barbieri, 2009).
List of Clinical Correlates
- Polar body biopsy
- Preimplantation genetic diagnosis
- Twinning
- Prenatal diagnosis
- Assisted reproductive technology
References
Dorland, W. (2011) Dorland's Illustrated Medical Dictionary. 32nd edn. Philadelphia, USA: Elsevier Saunders.
Gitlin, S. A., Gibbons, W. E. and Gosden, R. G. (2003) 'Oocyte biology and genetics revelations from polar bodies', Reprod Biomed Online, 6(4), pp. 403-9.
Meneely, P. M., Hoang, R. D., Okeke, I. N. and Heston, K. (2017) Genetics: Genes, Genomes, and Evolution. Oxford University Press.
Schmerler, S. and Wessel, G. M. (2011) 'Polar bodies--more a lack of understanding than a lack of respect', Molecular reproduction and development, 78(1), pp. 3-8.
Strauss, J. F. and Barbieri, R. L. (2009) Yen and Jaffe's Reproductive Endocrinology: Physiology, Pathophysiology, and Clinical Management. Saunders/Elsevier.
