What is mitosis and meiosis

Mitosis

• Mitosis is a continuum of changes but biologists like break down the stages of mitosis into four main stages, prophase, metaphase, anaphase and telophase.
• The focus in this class is on an understanding of the process and not a memorization of phases.
• The only phase name you will need to remember is metaphase.
• In mitosis the nuclear membrane is broken down, spindle fibers (microtubules) attach to the chromatids at the centromere and pull apart the chromatids.
• When the chromatids reach separate ends of the cells the spindle fibers disintegrate and a nuclear membrane rebuilds around the chromosomes making two nuclei.
• Each nucleus is identical to the original nucleus as it was in G1.

Meiosis

• Meiosis is the form of nuclear cell division that results in daughter cells that have one half the chromosome numbers as the original cell.
• In organisms that are diploid, the end result is cells that are haploid. Each daughter cell gets one complete set of chromosomes, i.e., one of each homologous pair of chromosomes.
• In humans this means the chromosome number is reduced from 46 to 23.
• The only cells that undergo meiosis will become sperm or eggs.
• The joining together of a sperm and egg during fertilization returns the chromosomes number to 46.
• Cells that undergo meiosis go through the cell cycle including the S phase so begin the process with chromosomes that consist of two chromatids just as in mitosis.
• Meiosis consists of meiosis I and meiosis II. In meiosis I homologous chromosomes are separated into different nuclei.