Main Difference – Mitosis vs Meiosis
The words mitosis and meiosis can be confused by some as they seem a bit alike. Both these processes denote the chromosome division followed by a cell division (cytokinesis). In mitosis, a single nuclear division (karyokinesis) and cell division take place whereas in meiosis two nuclear and cell divisions take place (meiosis I and meiosis II). At the end of mitosis, the chromosome number in daughter cells are equal to the number in original cell (mother cell); however, in meiosis, daughter cells receive half the number of chromosomes from the mother cell. This can be considered as the main difference between mitosis and meiosis.
What is Mitosis
Mitosis consists of five stages, prophase, prometaphase, metaphase, anaphase, and telophase and cytokinesis.
Prophase
Each chromosome in a prophase cell consists of two sister chromatids attached to one centromere. In this stage, chromosomes become more condensed and, therefore, can be seen under a light microscope. At this stage, mitotic spindle, microtubules move the chromosome within the cell forms. And also spindle grows out from a pair of centrosomes and grows towards the opposite end of the cell. However, this structure cannot be observed in some plant cells.
Prometaphase
Prometaphase starts with the degeneration of nuclear membrane. Some spindle fibers are attached to the centromere regions of the chromosomes. Microtubules are attached to the either side of the sister chromatids, to kinetochores. Then the other end of these microtubules gets attached to the centrosome of the opposite poles.
Metaphase
In this phase, chromosomes arrange along the center of the cell, metaphase plate as a single line.
Anaphase
After the metaphase connection between sister chromatids breaks down, the chromatids start to move to the opposite direction from each other, i.e., towards centrosomes. Special proteins called molecular motor proteins disassemble tubulin molecules in the spindle and generate force so that chromosomes are pulled towards the opposite poles.
Telophase
Once the chromatids move to the spindle poles, the chromatids are referred to as chromosomes. In the telophase, nuclear membrane re-forms around each set of chromosomes and produces two distinct nuclei within the cell. Chromosomes also start to relax; therefore, the condensation disappears. Generally telophase is followed by the cytokinesis.
What is Meiosis
Meiosis is composed of two cell divisions: meiosis I and meiosis II. Meiosis I has five stages, prophase I, metaphase I, anaphase I, telophase I. Meiosis II also consists of five stages prophase II, metaphase II, anaphase II, and telophase II.
Meiosis I
Prophase I
Longest stage in meiosis I. This stage is subdivided into five stages as,
Leptotene – condensation of chromosomes occur, and they become visible
Zygotene – while condensing homologous chromosomes pair up. And synapsis, close association occur between homologous pairs.
Pachytene – chromosomes become shorter and thicker and synaptonemal complex become more visible
Diplotene – centromeres of the paired chromosomes move apart
Diakinesis – further condensation of chromosomes occurs
Metaphase I
Homologous chromosomes are aligned along the metaphase plate. Microtubule from one pole attaches to one centromere and the opposite end microtubule attach to the other homologous pair of the chromosome.
Anaphase I
A homologous pair of the chromosomes moves towards the opposite ends from each other, i.e., towards spindle end.
Telophase I
Chromosomes arrive at the spindle end and cytoplasm divide.
Meiosis II
As in prophase I of meiosis, prophase II starts with thickening of chromosomes, the disappearance of the nuclear envelope and the formation of spindle fibers. Then in metaphase II, chromosomes arrange singly on the metaphase plate, and spindle fibers from two opposite centrosomes get attached to the centromeres. The new metaphase plate is rotated by 90o when compared to the metaphase I of meiosis I. During anaphase II, centromeres divide and chromatids pull towards opposite ends. In telophase II, chromosomes relax, nuclear envelope forms, spindle fibers disassemble, and finally cytokinesis takes place resulting four daughter cells.
Difference Between Mitosis and Meiosis
Definition of Mitosis and Meiosis
Mitosis is a cell division method that produce two daughter cells that have an equal number of chromosomes to the mother cell and identical to the mother cell.
Meiosis is a cell division method that produce four daughter cells that has half the number of chromosomes from the mother cell and genetically different from the mother cell.
Discovery
Mitosis was discovered by German Biologist Walther Flemming
Meiosis was discovered by German Zoologist Oscar Hertwig
Function
Mitosis helps in the development of organisms, repairing of cells, and healing.
Meiosis helps in the formation of gametes.
Type of Cells
Mitosis involves Somatic cells.
Meiosis involves Germ/reproductive cells.
Number of Divisions
There are two divisions in Mitosis
There is only one division in Meiosis.
Number of Daughter Cells
Mitosis produces two daughter cells.
Meiosis produces four daughter cells.
Ploidy Level
Mitosis’s ploidy level is Diploid.
Meiosis’s ploidy level is Haploid.
Genetic Composition
The genetic composition of Mitosis is identical to the mother cell.
The genetic composition of Meiosis is different from the mother cell.
DNA Replication
DNA replication of Mitosis occurs in interphase.
DNA replication of Meiosis occurs in interphase 1.
Stages of Prophase
In Mitosis, prophase has no phases.
In Meiosis, prophase is dived into 5 sub-stages: Leptotene, Zygotene, Pachytene, Diplotene, and Diakinesis.
Pairing of Homologous Chromosomes
In Mitosis, homologous chromosomes do not pair.
In Meiosis, homologous chromosomes pair.
Crossing Over
In Mitosis, there is no cross over.
In Meiosis, crossing over between homologous chromosomes can be seen.
Synapsis and Synaptonemal Complex
In Mitosis, there is Synapsis or synaptonemal complex.
In Meiosis, Synapsis and synaptonemal complex take place during prophase.
Chromosome Arrangement in Metaphase Plate
In Mitosis, Chromosomes arrange singly on the metaphase plate.
In Meiosis, Homologous chromosomes arrange in two parallel lines besides the metaphase plate.
Centromere Division
In Mitosis, centromere division occurs in anaphase.
In Meiosis, there is no centromere division in anaphase I. However, centromeres divide in anaphase II.
Cytokinesis
Cytokinesis follows every Mitosis.
In Meiosis, cytokinesis usually occurs after the telophase II.
References:
Pierce, B.A. (2012), Chromosomes and Cellular Reproduction (4th edition), Genetics A Conceptual Approach
Image Courtesy:
“Mitosis schematic diagram-en” by Schemazeichnung_Mitose.svg: Jpablo cadtranslation: Matt (talk) Diagrama_Mitosis.svg: juliana osorio derivative work: M3.dahl (talk) –(CC BY-SA 3.0) via Wikimedia Commons
“Meiosis diagram” by Marek Kultys – Own work.(CC BY-SA 3.0) via Commons
