Mitosis is the division of a cell to create two identical daughter cells, whereas meiosis forms daughter cells that are different than the parent cell. Mitosis is a means of replacing old cells; meiosis forms sex cells, or gametes.
At the beginning of mitosis, chromosomes become visible in the nucleus of the cell. The nuclear membrane dissolves and special fibers, the spindle, line the chromosomes up across the middle of the cell. Pairs of chromosomes move to opposite ends of the cell and new nuclear envelopes form around them. The chromosomes decondense, becoming invisible again as the entire cell splits down the middle. The result of this process is two identical daughter cells.
The beginning of meiosis is similar to mitosis, except that homologous, or like, chromosomes pair up. The chromosome pairs consist of one chromosome of each parent. Like mitosis, the nuclear envelope disappears and spindle fibers form to align chromosomes and pull them to opposite ends of the cell. The alignment of homologous chromosomes in meiosis is random, meaning that daughter cells can get chromosomes from either parent. This is one source of genetic diversity in sexual reproduction. Another source is that the homologous chromosomes, while in their pairs, trade genetic material with one another, further increasing genetic diversity. Meiosis ends much like mitosis, but instead of identical cells, the result is two distinctly different daughter cells.