Meiosis
It is a kind of cell division in which sexually reproducing organisms produce gametes like sperm and egg cells. It further undergoes two divisions which result in the formation of four daughter cells. In this kind of division, the number of chromosomes is reduced to half and produces four gamete cells.
This cell division occurs in diploid parents cells which shows it has two daughter cells. In the case of diploid parents, they undergo one DNA replication and two types of meiosis cell division i.e. meiosis 1 and meiosis 2. These two meiotic divisions lead to the formation of four haploid daughter cells which means they consist of half chromosomes of the diploid parent cell.
Type of Meiosis Division
Meiosis cell division takes place in two stages, they are:
Meiosis I:
It is further divided into different Kinds, they are
A. Prophase I:
In this step there occurs disintegration of the nuclear envelope and chromosome condensation starts. They also occur in the appearance of spindle fibre.
B. Prometaphase II:
In this phase there occurs alignment of homologous chromosomes at the equatorial plate which ensure genetic diversity among offspring.
C. Metaphase I:
In this phase homologous chromosomes align at the equatorial plate ensuring genetic diversity among offspring.
D. Anaphase I:
The homologous chromosomes are pulled towards the opposite poles.
E. Telophase I:
In this phase there occurs the disappearance of spindle fibre and by the nuclear envelope reform.
F. Cytokinesis I:
In this phase, two non-identical diploid cells are formed by the segregation of cytoplasm.
Meiosis II:
This is meiosis is further divided into different Stages:
A. Prophase II:
In this phase, chromatin condenses into chromosomes and disintegration of the nuclear envelope occurs. In this phase migration of centromeres occurs to either pole which leads to the reformation of spindle fibre.
B. Metaphase II:
In this phase, chromosomes align themself along the equatorial plate.
C. Anaphase II:
In this phase sister chromatids are pulled towards the opposite pole.
D. Telophase II:
In this phase nuclear envelope undergoes redevelopment and spindle fibre disappears.
E. Cytokinesis II:
At last in this cytokinesis phase cytoplasm and the cell divides and produces four non-identical haploid daughter cells.
At the end of cell division, we are left with four non-identical haploid daughter cells.
FAQs on Meiosis Definition
Q1. Explain for which two reasons, we get genetically different gametes by meiosis division?
Ans. Crossing over: It is a point where crossing over of homologous chromosome occurs and the exchange of genetic material occurs randomly and this process is different in each cell that goes through meiosis.
Random orientation of homologous pairs: In metaphase 1, the random orientation of homologous pairs occurs. By this, there occurs production of gametes with many different assortments of homologous chromosomes.
Q2. Why is meiosis I different from Meiosis II ?
Ans. In the case of meiosis I, separation of the homologous chromosome takes place whereas in the case of meiosis II there occurs the separation of sister chromatids.
In meiosis I two daughter cells are formed whereas, in meiosis II, four daughter cells are formed.
