DIFFERENCE BETWEEN MITOSIS AND MEIOSIS

                           

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Question: What are the principal differences between mitosis and meiosis?

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Major differences between mitosis and meiosis.

Answer:

The major two types of cell division i.e. mitosis and meiosis which give rise to new cells, occur in different types of cells having different functions and thus exhibit some differences when compared. They are: 

Difference between mitosis and meiosis: Diagram

The main difference between mitosis and meiosis:

The major differences between mitosis and meiosis are as follows: 

1. Mitosis occurs in all somatic cells while meiosis is limited to germinal cells only.
2. Homologous chromosomes come together i.e., synapsis occurs only in meiosis.
3. In Mitosis, one replication cycle of DNA is followed by 1 division, resulting in diploid cells. whereas in meiosis one replication of DNA is followed by two divisions resulting in haploid cells.* Meiosis consists of two successive cell divisions, but the chromosomes reproduce (i.e., the DNA replicates) only before the first division( meiosis I).
4. In Mitosis, DNA replication occurs in the S-phase, which is followed by G2. In meiosis, there is a pre-meiotic DNA synthesis, which is very long and followed immediately by meiosis.
5. In Mitosis, each chromosome is independent, while in meiosis there is the pairing of homologous chromosomes.
6. Mitosis lasts 1to2 hours whereas meiosis lasts longer; in males, it may last 24 days and in females several years.
7. In mitosis, the genetic material remains constant and in meiosis, there is genetic variability.

Difference between Mitosis and Meiosis table:

  

Points of difference	Mitosis	Meiosis
Occurrence	It occurs almost in all types of (somatic)cells	Occurs mainly in reproductive parts of sexually reproducing organisms
Number of divisions	The process is completed in one division only.	The process is completed by two successive divisions.
Nature of cells produced	Two identical daughter cells are produced from a single mother cell	Four daughter cells are produced from a mother cell.
The chromosome number	Remains the same as that of the parent cell (equational division).	Reduced to half (haploid) in the four daughter cells produced from the parent cell (reductional division).
Division of chromosomes	The chromosomes divide once along with one cell division.	Chromosomes divide once along with two cell divisions.
Nature of prophase	It shows one short and simple division without any sub-divisional stages	Prophase is composed of two divisions. Prophase I is prolonged and complicated with five sub-divisional stages i.e. leptotene,  zygotene, pachytene, diplotene and diakinesis. Prophase II is just like mitosis prophase.
Division of centromere during prophase	During prophase, each chromosome is divided into two daughter chromatids but the centromere remains undivided.	Chromosomes remain undivided along with centromere.
Synapsis	No synapsis between homologous chromosomes.	Synapsis occurs between homologous chromosomes.
Crossing over	No crossing over and no chiasma formation so no exchange of genetic material.	Crossing over and chiasma formation takes place causing an exchange of genetic material between non-sister chromatids of homologous chromosomes.
Position of Centromere during prophase	The centromere usually lies at the equatorial plane and the arms point towards the two poles.	The centromeres of homologous chromosomes lie equidistant from the equator and extend towards the pole in metaphase I but in metaphase II, the centromeres remain at the equatorial plane.
Nature of metaphase chromosome	The chromatids remain diad.	The chromatids of homologous chromosomes remain as tetrad.
Status of centromere during metaphase	The centromere divides longitudinally leading to the separation of chromosomes.	There is no need for centromeric division in metaphase I but the centromere divides like mitosis in metaphase II.
Movement of chromosomes during Anaphase	The longitudinal segments of chromosomes ( monads) move towards the two poles.	In Anaphase I there is movement of the entire chromosome with exchanged segments toward poles but in Anaphase II the movement is the same as Mitosis.
Telophase chromosome number	The chromosome is identical in the parent and daughter nuclei.	Chromosome number is reduced to half in the daughter nuclei after Telophase I but after Telophase II, the daughter nuclei with identical chromosome numbers are produced.
Appearance of nucleolus and nuclear membrane	Nucleolus and nuclear membrane appear at the end of telophase	They appear temporarily at the end of telophase I but permanently at the end of telophase II.
Status of telophase chromosomes	The chromosomes of the daughter cells are without genetic recombination.	In the four haploid daughter cells, half the chromosome is crossover type while the other half is non-crossover type.
Product of cytokinesis	Two diploid daughter cells.	Four haploid daughter cells.
Nature of cytokinesis	The cytokinesis is conspicuous ( easily seen) after karyokinesis occurring along with nuclear division in animal cells	The cytokinesis I is very much inconspicuous but the cytokinesis II is of usual occurrence.