What happens in meiosis?
You have learned that in meiosis we are going to have to take a diploid cell (2N) and make haploid (N) daughter cells from it. These daughter cells are then going to have to be able to act as gametes for sexual reproduction. In order to accomplish this task, meiosis requires two physical cell divisions within it to occur. I have diagrammed these divisions here.
In this drawing, the parent cell (the one on top) is diploid. It divides in the first division (called Meiosis I) into 2 daughter cells. The daughter cells, which are already haploid, then go through the second division (called Meiosis II) into a total of 4 daughter cells. These final daughter cells are haploid, but can also act as gametes.
Each meiotic division will go through similar steps to what you learned about for mitosis. So each has a prophase, metaphase, anaphase, and telophase. These are just now numbered to identify which meiotic division they are in, like: prophase I, metaphase I, anaphase I, and telophase I are in meiosis I, while prophase II, metaphase II, anaphase II, and telophase II are in meiosis II. So in each division you are going to: 1) condense your DNA; 2) organize your DNA; 3) split your DNA into two groups; and 4) decondense your DNA.
Because the reduction in chromosome number occurs in Meiosis I, as we go from diploid to haploid cells, Meiosis I is called the "reduction division." You might be wondering why we need a second division. Well, that should become clear as you keep learning about meiosis.
You will see as you learn more and more about meiosis, that all the weird stuff happens in Meiosis I. By weird, I mean all the stuff that is different from mitosis. Meiosis II will seem very similar to mitosis, and will be very easy to learn. But another part of meiosis I being weird is from the fact that you know that we have to jumble up our genetic information to make gametes with random alleles in them-- this all happens during meiosis I and is called genetic recombination.
I have written up the details of meiosis in two pages. A step-by-step meiosis page and then another page just to describe genetic recombination.
© 2006 STCC Foundation Press, content by Dawn A. Tamarkin, Ph.D.
Last changed: January 21, 2007