Meiosis (Cell Division via Meiosis)
Background:
This follows the introduction to cell division.
Reminder: Meiosis, which is also referred to as 'reduction division', is the form of division of the cell nucleus by which a cell divides into four 'daughter cells' each of which has half** of the number of chromosomes of the original cell. Meiosis only occurs in the gametes and is prior to the formation of sperm in males and ova in females.
**The cells return to having the normal (called 'diploid') number of chromosomes after fertilization of the ova by the sperm.
The difference that mitosis leads to TWO daughter calls (identical to each other and to the original cell), whereas meiosis leads to FOUR daughter cells each of which has half of the number of chromosomes of the original cell.
So, meiosis is the type of division of cell nuclei that occurs specifically to produce the gametes, which are mature sex cells: Ovum in the female and the spermatozoon in the male. These are for sexual reproduction. The complete production of gametes, including both the cell division stage and the subsequent maturing of the gametes is called gametogenesis.
The Stages of the 'Cell Cycle' for Reproductive Cells
In all reproductive cells, that is in all cells relating to the reproductive parts of the body, the 'cell cycle' consists of four periods : Two 'interphase' periods in which the cell is not dividing, and two 'meiotic' phases in which the cell is dividing:
Sequence:
- Interphase I
- Meiotic Phase I, consisting of:
(a) Meiosis (Nuclear Division I) - Prophase, Metaphase, Anaphase and Telophase, followed by
(b) Cytokinesis (Cytoplasmic Division I). - Interphase II
- Meiotic Phase II, consisting of:
(a) Meiosis (Nuclear Division II) - Prophase, Metaphase, Anaphase and Telophase, followed by
(b) Cytokinesis (Cytoplasmic Division II).
Due to this longer sequence of events, meiosis is the more complex of the two types of cell division.
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Notes:
- Meiosis involves two successive divisions (both of which include division of the cell nucleus, followed by division of the cell cytoplasm). They are called the First Meiotic Division and the Second Meiotic Division.
- Each of these successive cell divisions may be described in terms of four phases - called prophase, metaphase, anaphase and telophase.
- The first meiotic division is similar to mitosis and the second meiotic division is the 'reduction' stage, which differs slightly according to whether male or female gametes are to be produced.
- Meiosis enables the exchange of genetic material between chromosomes. This takes place during the early prophase phase of the first meiotic division.
See also related pages about Cell Structure, Introduction to Cell Division, Mitosis and the Diagram of Mitosis.
