Biology
Topic: Meiosis As A Type Of Cells Division
Table Of Contents
- Meaning Of Meiosis
- Stages Of Meiosis
- Importance Or Role Of Meiosis
What Is Meiosis?
Meiosis is a two successive cell division with only one duplication of chromosomes. Four daughter cells are produced in meiosis. Meiosis is a reduction in cell division and the resulting four daughter cells are haploid.
Meiosis takes place in reproductive cells, i.e., ovules and pollen grains in plants, ovaries and testes in animals. In animals, meiosis occurs in the formation of gametes (sex cells such as eggs and spermatozoa).
The process of gamete formation is called gametogenesis. The process involved in the production of spermatozoa by testes is called spermatogenesis while that of eggs or ova production by the ovaries is called oogenesis.
Stages of Meiosis
Meiosis consists of two successive divisions:
a. Ist meiotic division- when the parent cell splits into two.
b. 2nd meiotic division- when the products then divide again giving a total of four daughter cells.
1st Meiotic Division or Reduction Division
This Ist meiotic is divided into five stages:
1. Interphase: This is the resting stage of the cell. At this stage, the chromosomes are not seen.
2. Prophase 1: Prophase 1 is divided into three:
a. Early prophase 1: At this stage, the chromosomes contract, becoming more clearly visible and the nucleus shrinks.
b. Mid prophase 1: The homologous chromosomes come together (synapsis) forming a bivalent.
c. Late prophase 1: During this stage, each chromosome is seen to consist of a pair of chromatid. At prohase 1, crossing over takes place. The points on the chromosomes where crossing over takes place are known as chiasmata. (singular form is called chiasma).
3. Metaphase 1: During metaphase 1, the nuclear membrane disappears and the spindle is formed. The bivalents (chromosomes) assemble at the equatorial region of the spindle.
4. Anaphase 1: At this anaphase, the bivalents separate completely and each member chromosome moves to the opposite pole of the spindle.
5. Telophase 1: This stage produces two daughter cells with chromosome number, halved as in the parent cells.
2nd Meiotic Division
The second meiotic division is made up of four stages. The division is similar to mitosis. At the end of the second division, four groups of daughter cells are formed:
1. Prophase 11: The daughter cells prepare for the second meiotic division. Here, the centrioles have replicated and a new spindle is formed.
2. Metaphase 11: The chromosomes arrange themselves on the spindle in the usual way. The chromosomes appear doubled and the centromere starts to divide in the position of the equatorial plane.
3. Anaphase 11: Each chromosome finally splits into two. The actual chromosomal division takes place ate anaphase 11 and each one moves to opposite poles of the cells.
4. Telophase 11: The two cells are divided into four which is tetrad. The four haploid cells are produced from the original diploid mother cell.
Importance Or Role Of Meiosis
The importance of meiotic process are:
1. It aids the formation of sperms or male gametes in animals.
2. It aids the formation of ova (eggs) or female gametes in animals.
3. It aids the formation of pollen grains in anthers of flowering plants.
4. It also aids the formation of ovules in ovary of flowering plants.
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