The Stages of Mitosis: One Cell Becomes Two

0:00How does one cell divide to make two identical cells?

0:05The answer is mitosis. Here is one cell: its cell membrane, cytoplasm and nucleus.

0:13Inside the nucleus are chromosomes, long threads of DNA.

0:18To keep it simple, this cell has just four chromosomes: a long pair and a short pair.

0:24Before mitosis, in interphase, the cell copies every chromosome. DNA is not copied during mitosis.

0:33First, in prophase, the copied chromosomes coil up and become short and thick.

0:40Each is now two identical copies, called sister chromatids, joined together.

0:46The nuclear membrane breaks down, and thin threads called spindle fibres form.

0:52In metaphase, the chromosomes line up across the middle of the cell.

0:57In anaphase, the fibres pull the sister chromatids apart, to opposite ends of the cell.

1:03Each end now has one copy of every chromosome: two long and two short.

1:09In telophase, a nuclear membrane forms around each set, and the chromosomes uncoil.

1:16Then, in cytokinesis, the cytoplasm and cell membrane divide, making two cells.

1:23Each new cell has the same four chromosomes as the parent, so they are identical.

1:29A human body cell has 46 chromosomes, and each new cell from mitosis has 46 too.

1:37Mitosis is used for growth, repair and asexual reproduction, which makes identical offspring.

1:44In short, mitosis turns one cell into two cells with identical chromosomes.