“In biology, nothing is clear, everything is too complicated,everything is a mess, and just when you think you understand something, you peel off a layer and find deeper complications beneath. Nature is anything but simple.” By Richard Preston. Let this statement not scare you on biology.
Mitosis: In cell biology the process of nuclear division is mitosis. During division the nucleus of the cell separates into two sets of identical chromosomes or organised DNA proteins.
A nucleus is a membrane structure that contains a cell’s hereditary information.
A further process in the cell division called cytokinesis, divides the cells to two totally separate cells called the daughter cells.
The main purpose of mitosis is natural growth of organisms. Worn out, damaged cells are replaced with this process. An example of an animal which uses this process is the lizard. They regrow their tails after they have been cut.
Meiosis: A Greek word meaning small it takes its name from meioun. It is a cellular division but happens in specific type of reproductive cell called gametes. The specialised cell forms reproductive cells such as spores in plants or sperms in human.
In meiosis the DNA from each contributing cell gets mixed up with other little DNA’s from different cells forming parts of the X. The number of chromosomes created in each gamete is reduced from the diploid cell. Chromosomes determine the physical characteristics of a child in the event a pregnancy occurs.
Compare and Contrast Mitosis and Meiosis
Type of reproduction Sexual Asexual
Genetic Different Identical
Definition Type of cellular reproduction in which number of chromosomes are reduced by half through separation of homologous chromosomes producing two haploid cells An assexual reproduction process in which the cells divides into two producing a replica, with an equal number of chromosomes in each diploid cell
Crossing over Mixing of chromosome can occur Crossing over cannot occur
Number of divisions 2 1
Occurs in Human, fungi , plant animals All organisms
Number of daughter cells produced 4 Haploid cells 2 Diploid cells
Paringi of homologs Yes No
Chromosome number Reduced by half Remains the same
Function Genetic diversity through sexual reproduction Cellular reproduction and general growth and repair of the body
Karyokinesis Occurs in interphase 1 Occurs in interphase
Cytokinesis Occurs in telophase 1 and in telophase 2 Occurs in telophase
Creates Sex cells only, male sperm cells or female egg cells Makes every other cell other than sex cells
Centromeres split Centromeres does not separate during anaphase 1 but during anaphase 2 Centromere splits during anaphase
Discovered by Oscar Hertwig Walther Flemming
Stages of Mitosis and Meiosis
Mitosis: Has a four stage process. The entire four stage process takes about an hour in duration for the division to complete. The steps follow one another without pause.
Interphase: Chromosomes are dispersed in the nucleus and they appear as chromatin, a network of long thin threads or filaments. The chromosomes replicate to form pairs of identical chromosomes called chromatids. The DNA is synthesised only during interphase stage.
Prophase: The two chromatids remain attached at the centromere. In this phase the spindle begins to form. In animal cells the centrioles separate and become apart radiating asters which are bundle of fibers. Some fibers run from one centriole to another. This are called spindle fibers. In plants the spindles form without the centrioles.
Metaphase: Chromosomes congregate between two ends of which the spindles taper. The equatorial plane is the point where the cell will divide when nuclear division is complete. The chromatids are attached to the spindle fibers at the centromere.
Anaphase: The two chromatids of each chromosome separate at this stage and move to opposite poles. During Telophase new nuclear envelopes form around two groups of daughter chromosomes, and the nucleoli will begin to appear. As the formation of the nuclei is complete the spindle disappears. Cytokinesis which may begin before or after mitosis is completed and finally separates the daughter nuclei to two individual daughter cells.