Mitosis vs Meiosis: Key Differences and Examples
You might recognize that mitosis and meiosis are similar in name and have other similar components that make it difficult to differentiate between. Generally, for an organism to grow, repair, and develop, its cells must either expand or undergo replication to create more cells. The latter, the process of replication, paves the way for another decision that cells must make: prepare for mitosis vs meiosis?
Mitosis and meiosis are the two different types of cell division. Generally, mitosis involves the cell creating another copy of itself to aid in growth and repair of the organism. Meiosis involves the new copies dividing again to contain half of the genetic material of the original cell – these cells function as sperm and egg cells that support the process of sexual reproduction.
What is Mitosis?
The process of mitosis involves the parent cell replicating its DNA and dividing into two daughter cells. Mitosis has 5 distinct phases: interphase, prophase, metaphase, anaphase, and telophase.
In Interphase, the DNA in the nucleus of the cell is replicated and results in two identical copies of its chromosomes. Two centromeres are located outside of the nucleus and play an integral role in cell division. During this phase, microtubules – structural components of the cell – will extend out of the centromeres.
In Prophase, the duplicated chromosomes condense to become smaller, more compact entities. The duplicated chromosomes move toward each other and pair up. Due to the replicated nature of the DNA, the sister chromatids are joined together at the centromere; under a microscope, the chromosomes appear to look like X-shaped bodies. The end of this phase signals the nucleus to dissolve and allowing the chromosomes to be released. The centromeres and the attached microtubules migrate to opposite poles of the cell to form the mitotic spindle, which will be responsible for the process of cell division.
In Metaphase, the chromosomes line up across the equator of the cell positioning themselves between the opposite centromeres. The highly dynamic microtubules of the mitotic spindle extend to attach to each of the centromeres of the sister chromatids.
In Anaphase, the binding components at the centromere that hold the sister chromatids together are broken down. This allows for the sister chromatids to be pulled apart at the centromere by the mitotic spindle and moved to opposite poles of the cell.
In Telophase, the chromosomes end up at opposite poles of the mitotic spindle and a new nuclear, membrane forms around these two new sets of chromosomes. During the process of cytokinesis, a split occurs at the center of the cell to produce two new daughter cells with identical genetic information.
What is Meiosis?
Meiosis has many similar components to mitosis but in meiosis, this process is tasked with separating sister chromatids but also with separating homologous chromosomes. During meiosis, cells go through division twice to produce 4 gametes (either sperm or egg cells).
Similar to mitosis, the DNA is replicated so that there are two copies of the chromosomes in the nucleus.
Here in Prophase I, we start to see differences between mitosis and meiosis. The chromosomes condense and become more compact but they also pair off so that they match up along their full length. Once lined up, the homologous (same) chromosomes position themselves on top of each other, break DNA off at the same part, and trade the corresponding DNA during a process called crossing over. This process leads to new, diverse chromosomes with differentiated genes and alleles. Similarly to mitosis, the meiotic spindle forms and migrates to opposite sides of the cell. The nuclear membrane around the chromosomes dissolve and release them.
The chromosomes are shifted to the equator of the cell, and they bind to just one pole of the mitotic spindle. Essentially, each homologous pair binds to just one side of the meiotic spindle to prepare for separation; this is dissimilar to mitosis where the microtubules from each pole attach to the sister chromatids at the centromere.
During this phase, the homologous chromosomes are pulled to opposite ends of the cell; the sister chromatids of each chromosome remain attached and do not come apart.
The homologous chromosomes end up at opposite ends of the cell where the cell prepares for cytokinesis as it is pinched apart in the middle. This results in two haploid daughter cells that prepare for Meiosis II.
During meiosis II, DNA replication does not occur again – it is helpful to consider that meiosis II is just mitosis for the haploid cells formed in meiosis I. During meiosis II, the sister chromatids in each haploid cell will be divided to form 4 cells.
The chromosomes condense once again into compact bodies and the mitotic spindle is formed once again. The microtubules attach to each sister chromatid of the chromosomes.
The chromosomes are lined up at the equator of the cell.
During this phase, the mitotic spindle pulls the sister chromatids away from each other to opposite ends of the cell.
A nuclear membrane is formed around the new sets of chromosomes and the chromosomes enlarge back to the original size. Finally, cytokinesis occurs once again to form 4 haploid cells with chromosomes containing only one chromatid.
Key Takeaways from Mitosis vs. Meiosis
· Mitosis is responsible for producing new identical cells to the parent cell to aid in repair and growth (ex. Can be used to produce new cells in damaged tissues).
· Two new cells with two identical sets of chromosomes (diploid) are formed.
· Mitosis undergoes cell division or cytokinesis once.
· Mitosis occurs for somatic or body cells.
· Meiosis is responsible for producing gametes or sex cells that aid in sexual reproduction. In humans, these sex cells are either sperm or egg cells.
· Four cells with differentiated genetic information are formed. These cells each have a single set of unpaired chromosomes.
· Meiosis undergoes cell division or cytokinesis twice.
· Meiosis occurs for germ cells (sex cells).
By Aishwarya Chitoor