Meiosis

Figure 60.

Prophase takes up over half of all mitosis. There is the breakdown of the nuclear envelope and the nucleolus disintegrates. The centrosome duplicates itself to make two daughter centrosomes. These centrosomes form the mitotic spindle. The chromosomes become compacted. Each replicated chromosome can be seen as two separate chromosomes. The chromosomes are held together by a centromere.

Prometaphase involves migration of the of the chromosomes to the equatorial plate called the metaphase plate. This forms a kinetochore structure on each side of the centromere. There is a continual condensation of the chromosomes. This leads to metaphase, in which the chromosomes align along the metaphase plate.

Anaphase is the shortest phase. It is when the centromeres divide and the sister chromatids are pulled apart. The microtubules pull these sister chromatids to the opposite side of the cell. The sister chromatids are then referred to as daughter chromosomes. Telophase happens when the nuclear envelope is remade and chromosomes become diffuse again. Cytokinesis is the actual separation of the two cells. A cell plate forms in cytokinesis involving plants.

MEIOSIS

Meiosis is an aspect of eukaryotic cell division that makes haploid sex cells also called gametes from cells that are diploid or those that contain two copies of each chromosome. There are two parts to meiosis called meiosis I and meiosis II. There is

DNA replication followed by separation into cells that become haploid cells. Figure 61 shows the process of meiosis:

Figure 61.

Meiosis I will separate the pairs of homologous chromosomes. There are several phases to this, including prophase I, metaphase I, anaphase I, and telophase I, followed by cytokinesis. It is during prophase I that crossing over and recombination of the genes