Meiosis

MeiosisAn introduction by Ben Kwok

Interphase ILike mitosis, meiosis is preceded by an Interphase. During this time, DNA replicates and each chromosome becomes doubled, consisting of two different strands of DNA.

Prophase IDuring Prophase, chromosomes cross over and exchange DNA. After crossing over has occurred, the sister chromatids are no longer identical to one another. Spindle fibers also form.

Metaphase IDuring Metaphase, chromosomes line up along the equator of the cell. Once the chromosomes are lined up, the ends of the spindle fibers attach to each centromere.

Anaphase IDuring Anaphase I, the chromosomes are pulled away from each other by the spindle fibers, to the opposite poles of the cell. At this point each chromosome is still double stranded.

Telophase IIn Telophase I, the spindle fiber disintegrates and cytokinesis (cell division) begins. Two cells are created, each cell with half the number of chromosomes of the original.

Prophase IIProphase II marks the start of Meiosis II, which is now pretty much normal mitosis. We now have two cells each with two chromosomes. In this stage, the spindle fibers again start to form at the poles of the cell. NOTE: DNA is not replicated.

Metaphase IIIn Metaphase II, the chromosomes line up along the equator, and spindle fibers attach to the centromeres.

Anaphase IIIn Anaphase II, the now separated chromatids approach their respective poles.

Telophase IIIn Telophase II, along with cytokinesis, we see the formation of 4, genetically different cells, each with half the number of chromosomes of the parent cell. This concludes Mieosis.