Mitosis

In biology specificly genetics, Mitosis is the process of eucaryotic cell replication which takes place to the majority of the cells in our body, producing identical copies of the genetic material in each new cell. This is different from meiosis, where the new cell produced has half the normal number of chromosones - a mixture of each parents' genes.

Mitosis in eukaryotes consists of nuclear division (the division of the cell nucleus) and cytokinesis (the separation of the two daughter cells), and consists of different phases. The phase between nuclear divisions, called interphase, is not technically part of mitosis. In animals, mitosis consists of the following steps:

• In prophase, the chromatin in the nucleus is being condensed into a "transport form" and becomes visible as chromosomes under the microscope. Centrioles move into position, the mitotic spindle is formed. The nucleolus becomes invisible.
• During prometaphase, the nuclear membrane dissolves. Kinetochores are build at the centromeres, and microtubuli are attached, starting to pull the chromosomes into position.
• In metaphase, the chromosomes are aligned along the metaphase plate in the middle of the cell by spindle fibers.
• Anaphase is the phase in which the chromosomes are separated, driven by both spindle microtubules and polar microtubules.
• During telophase, the chromatids arrive at opposite ends of the cell, where new nuclear membranes are formed around them. The chromatids are unfolded into usable form again.
• Cytokinesis is the actual separation of the two new cells.

The whole procedure is very similar among other eukaryotes, but some minor details vary. For instance, centrioles are not always present, and in many protists (e.g. ciliates) the nuclear membrane does not dissolve. Since prokaryotes do not have a nucleus or a nuclear membrane, and possess only a single chromosome, prokaryotic mitosis is more simple.

The genetic material in humans is in the form of 46 chromosones. The chromosones line up in the middle of the cell and are pulled in half by cell fibres. Because the arms of the chromosones are exact copies of each other each new cell still has the same genetic information. The new cells formed with these half-chromosones then develop membranes around the genetic material - becoming nuclei. The DNA then spreads out in each daughter cell into long strings and forms in to double-armed chromosomes.

See also : genetics -- cell biology -- meiosis -- cell cycle

/Talk