Meiosis I (Reduction Division)
* Homologous chromosome pairing and crossing over: In prophase I, homologous chromosomes (one from each parent) pair up and exchange genetic material through a process called crossing over. This creates new combinations of alleles (gene versions) on the chromosomes.
* Separation of homologous chromosomes: During anaphase I, the homologous chromosome pairs separate, moving to opposite poles of the cell. Each daughter cell receives one chromosome from each pair.
* Haploid cells produced: Meiosis I results in two daughter cells, each with half the number of chromosomes as the original cell (haploid).
Meiosis II (Equational Division)
* No homologous chromosome pairing or crossing over: Meiosis II doesn't involve pairing or crossing over.
* Separation of sister chromatids: In anaphase II, the sister chromatids (identical copies of a chromosome) within each chromosome separate and move to opposite poles.
* Four haploid cells produced: Meiosis II divides the two daughter cells from meiosis I, resulting in a total of four haploid cells.
In summary, the unique events of meiosis I that don't occur in meiosis II are:
1. Homologous chromosome pairing: This is essential for creating genetic diversity through crossing over.
2. Crossing over: This exchange of genetic material between homologous chromosomes shuffles alleles, creating new combinations.
3. Separation of homologous chromosomes: This halves the chromosome number, producing haploid cells.
Meiosis II is more like a mitotic division, separating sister chromatids to produce four haploid gametes (sperm or egg cells) ready for fertilization.
