In early fetal development, oogonia undergo numerous mitotic divisions. At birth, a woman's ovaries hold approximately one million primary oocytes. The primary oocytes begin to divide by meiosis before birth, replicating their DNA, but the cells enter the state of meiotic arrest. Having formed sister chromatids, the meiotic division is not completed until ovulation much later in puberty. During ovulation the meiotic divisions occur, but the two daughter cells of the first division are not equivalent. The secondary oocyte inherits nearly all the cytoplasm, with the other daughter cell, the first polar body, adhering to the secondary oocyte. The second meiotic division, in which the sister chromatids separate, occurs only after secondary oocyte is fertilized. One daughter cell again receives almost all the cytoplasm, the mature ovum, with the second polar body, the other daughter cell, being small and nonfunctional.

The WikiPremed MCAT Course is a comprehensive course in the undergraduate level general sciences. Undergraduate level physics, chemistry, organic chemistry and biology are presented by this course as a unified whole within a spiraling curriculum. Please read our policies on Privacy and Shipping & Returns.  Contact Us. MCAT is a registered trademark of the Association of American Medical Colleges, which does not endorse the WikiPremed Course. WikiPremed offers the customers of our publications or our teaching services no guarantees regarding eventual performance on the MCAT.

Creative Commons License
WikiPremed is a trademark of Wisebridge Learning Systems LLC. The work of WikiPremed is published under a Creative Commons Attribution NonCommercial ShareAlike License. There are elements of work here, such as a subset of the images in the archive from WikiPedia, that originated as GNU General Public License works, so take care to follow the unique stipulations of that license in printed reproductions.