Compare and contrast meiosis I and meiosis II. 

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txmedteach eNotes educator| Certified Educator

Meiosis I and II are pretty similar. Both involve cell division, and in both cases the resulting cells are haploid (containing one of each pair of chromosomes found in the diploid organism). The difference lies in the goal of each division and whether chromosomes are duplicated or not.

In Meiosis I, the goal is to produce haploid cells from diploid cells (2n, 2c) with a view towards eventually producing gametes. Here, there is chromosome duplication (still diploid, 2n, and double the DNA content, 4c), but instead of pairing up in the way they would for mitosis (where the resulting cells are diploid), they form tetrads, which are paired homologous chromosomes. During Metaphase and Prophase I, you get genetic recombination through "crossing over," where chromatids exchange DNA to allow for variation. During Anaphase I, the tetrads are pulled apart in such a way that the sister chromatids remain together, while homologues are pulled apart. After division, this results in two cells with a haploid number (n) of distinct chromosomes, but with copies of each chromosome (roughly the same amount of DNA as the original cell, notated 2c).

In Meiosis II, the goal is to produce the final gametes. Here, there is no duplication of chromosomes. The cells go right back into division-mode. The chromatids are separated in these haploid cells to produce two gametes each with the haploid number of chromosomes (n), and, now, with half the DNA of the original cell (c).

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