Different types of cell division occur in different parts of the body. Mitosis occurs in the somatic cells and meiosis occurs in the gametes. Each process has its biological purpose in living cells and this article focuses on the purpose of meiosis.
Growth and development are at the root of all forms of cell division. However, the different types meet different needs of cells. For instance, meiosis meets different needs in simple eukaryotes and multicellular organisms.
Ahead, this article discusses the process of meiosis, its purpose, and the risk of errors and disorders associated with them.
What is meiosis?
Meiosis is a process of cell division that produces gametes for sexual reproduction. At the end of the meiosis process, four haploid daughter cells are produced. These cells contain half the genetic material and chromosomes of the parent cells.
Meiosis is a specialized process that produces specialized cells such as ova, sperm, and pollen through the process of reduction division. When these cells join with other reproductive cells, they fertilize to produce a new diploid chromosomal complement.
In simpler terms, the meiosis process decreases the number of chromosomes from 46 to 23 in the reproductive cells. When two haploid reproductive cells fuse, the chromosome number is restored to 46 like the somatic cells.
Stages of meiosis
There are two stages of the meiosis process. They are meiosis I and meiosis II, and each stage consists of the prophase, metaphase, anaphase, and telophase phases. Each phase is labeled I or II according to the part it occurs in.
Meiosis I
Prophase I involves five unique stages (leptonema, zygonema, pachynema, diplonema, and diakinesis).
This is the longest part of meiosis and is characterized by a condensation of chromatin into visible chromosomes, the synapsis of chromosomes in each homologous pair, and a crossing over of genetic material between the chromosomes from the previous step.
Prophase I produce pairs of chromosomes called tetrads. Afterward, the tetrads go into metaphase I where spindle fibers on the centromere change their alignment to face each pole. In anaphase I, each tetrad splits into dyads (chromosome pairs) that are pulled to the opposite poles.
The first part of meiosis ends at telophase I where a nuclear membrane forms around the dyads.
The process of this first part of the meiosis process can be mistaken for mitosis. However, there are differences. In meiosis I, there is crossing over and chiasma formation, a pairing of homologous chromosomes, and a release of the cohesion sister chromatids.
Meiosis II
As mentioned earlier, both parts of the meiosis process occur in five stages. Meiosis II is very different from meiosis I. It involves the separation of sister chromatids to form four genetically distinct haploid cells with each cell containing one copy of each chromosome.
Each daughter cell from meiosis I form two daughter cells to produce the four haploid cells. Just before cytokinesis (the formation of four gametes), the nuclear envelope reappears, the spindle apparatus disappears and the chromosomes de-condense into chromatin.
The process of meiosis II shares more similarities with mitosis than meiosis I. However, meiosis produces four haploid cells instead of two. Also, it transfers only half the genetic material, unlike mitosis which transfers all the genetic material to the daughter cell.
What is the purpose of meiosis?
1. Production of reproductive cells
One of the primary functions of meiosis is producing gametes or reproductive cells that are responsible for reproduction. These germ cells in animals, egg cells, or sperm cells, develop into gametes. Plants also undergo meiosis to create spores, which later become the gametophytes that produce gametes.
The creation of gametes is necessary for passing on genetic information from one generation to the next. The formation of gametes ensures the survival of an organism.
2. Reduction of chromosome number
Another purpose of the meiosis process is to ensure that the haploid cells formed have half the number of chromosomes in the parent cell. The production of gametes is also important for halving the number of chromosomes in each haploid cell.
By reducing the number of chromosomes, each haploid cell contributes half set (n) to the resulting diploid (2n) zygote. The fusion of two haploid sets of chromosomes keeps chromosome number constant and ensures the passing on of accurate genetic information across generations.
Otherwise, chromosome numbers will double and be passed on to generations, causing chromosomal aberrations.
3. DNA damage repair
As cells prepare for meiosis, they first go through a process of DNA repair to correct any damages. Without removing or repairing genetic defects, incorrect information is passed on to the next generation and may manifest as harmful gene mutations, which could lead to cancer.
Meiosis involves a process called recombination. This step helps to replace defective alleles in a parent cell with the healthy alleles of the other parent. This way, healthy offspring are produced.
4. Genetic diversity
Meiosis involves the crossing over of homologous chromosomes to create new combinations of genes on chromatids. Crossing over or gene recombination allows genes from both parents to mix and either of them can be expressed in the offspring.
This process brings about genetic diversity across a population, thereby reducing the impact of genetic defects and the susceptibility of an entire population to diseases. Otherwise, one defect could eliminate an entire population.
Through genetic diversity, a population will include individuals that have strong adaptive features in a change of nutrient availability, harsh weather conditions, disease, or loss of habitat.
5. Prevention of chromosomal abnormalities
As said earlier, the production of gametes ensures that only half the number of chromosomes is contributed to the formation of a zygote. By preventing doubled chromosome content, medical conditions associated with meiosis errors can also be prevented.
Can there be errors in meiosis?
Cell division could go wrong. Meiosis errors occur when the cell produces an extra chromosome or is missing one chromosome. Errors in meiosis are common and have worse consequences than errors in mitosis.
The most common form is nondisjunction. This happens when chromatids do not separate during anaphase I or II. Consequently, there is an imbalance in the number of chromosomes present in each daughter cell.
Errors in meiosis affect reproduction in humans. It manifests as infertility and the formation of gametes with genetic defects. These errors are also the root cause of congenital abnormalities that affect newborns.
In germ cells like oocytes and spermatocytes, an error in chromosomal pairing could lead to a reduction in the number of these cells which will cause premature menopause in women and infertility in men.
Some medical conditions in humans associated with errors in meiosis are Down Syndrome, Patau Syndrome, Edwards Syndrome, Turner Syndrome, and Triple X Syndrome.
In addition, errors in the chromosomal pairing in yeast could lead to death.
FAQs
Are there cells that do not undergo meiosis?
Haploid cells cannot undergo meiosis because they are products of this type of cell division and they contain half the genetic material from the parent cells. Also, somatic cells do not undergo meiosis.
What is the most important part of meiosis?
Prophase I is the most important part of the meiosis process. This is the process of crossing over and genetic recombination. It is the longest part of this type of cell division and the success of the entire process depends on the success of prophase I.
What would happen without meiosis?
If cells do not undergo meiosis, the number of chromosomes will fluctuate across generations. It will result in too few or too many chromosomes and duplication of chromosome sets after every sexual reproduction.
In other words, there will be no effective sexual reproduction without meiosis.
What process precedes meiosis?
A cell must go through interphase before it enters meiosis I. The interphase consists of three identical phases: the G1, S, and G2. The cell grows in G1, replicates chromosomal DNA in the S phase, and prepares for division (meiosis) in G2.
Conclusion
Meiosis occurs in the gonads. The major aim of the meiosis process is to produce gametes for sexual reproduction. Unlike mitosis, the daughter cells in meiosis receive half the genetic material of the parent cells. As a result, each haploid daughter cell has its unique genetic formation.
One of the implications of meiosis is a reduction in the number of chromosomes in the gametes. The separate purpose of meiosis does not undermine its importance in living cells. However, it shows a level of cell specialization.
You can get a full grasp of the process and significance of cell division by also learning about the importance of mitosis.
Thanks for reading.