Synapsis is the pairing of homologous chromosomes during cell division, which is crucial for the proper segregation of chromosomes. During synapsis, two chromosomes that share the same size and shape (called homologous chromosomes) pair up to exchange genetic information.
As such, synapsis occurs only during prophase I of meiosis and not during mitosis. Instead, mitosis involves the duplication and separation of the chromosomes in the nucleus. During mitosis, the homologous chromosomes remain separate and do not exchange genetic information.
This article explains the process of synapsis, how meiosis and mitosis differ when it comes to the synapsis of homologous chromosomes, and the role of meiosis in genetic diversity.
What Is Synapsis?
Synapsis is the pairing of homologous chromosomes during cell division, which is crucial for the proper segregation of chromosomes.
During synapsis, two chromosomes that share the same size and shape (called homologous chromosomes) pair up and exchange genetic information. This process occurs in meiosis, which is unique because it involves two rounds of cell division, meiosis I and meiosis II.
In synapsis, the chromosomes align themselves closely together, forming a structure known as a tetrad, which are held together by a protein structure called the synaptonemal complex. This allows for the exchange of genetic material through a process called crossing over and is critical for genetic diversity.
During Which Phase Do Homologous Chromosomes Undergo Synapsis?
Homologous chromosomes undergo synapsis during prophase I of meiosis, the first and the longest phase of the process. During this phase, the nuclear envelope breaks down, and the chromosomes condense and become visible under a microscope. {1}
When Does Synapsis of Homologous Chromosomes Occur in Mitosis?
Synapsis, or the pairing up of homologous chromosomes to exchange genetic information occurs only in meiosis and not in mitosis. Instead, mitosis involves the replication and division of a cell’s chromosomes into two identical daughter cells.
Homologous chromosomes do not pair up during this process, and there is no exchange of genetic material. Also, in mitosis, homologous chromosomes don’t pair up and form bivalents like they do in meiosis.
The Role of Meiosis in Synapsis and Genetic Diversity
Meiosis, also known as reduction division, is a process of cell division that produces gametes — reproductive cells such as sperm cells and egg cells. Unlike mitosis, which produces two genetically identical daughter cells, meiosis produces four genetically diverse daughter cells.
Synapsis and the subsequent process of crossing over are vital in ensuring genetic diversity. Homologous chromosomes are pairs of chromosomes that have similar genes in the same order, but may have different versions (or alleles) of those genes.
For example, a person may inherit one allele for eye color from their mother and a different allele for eye color from their father. These two alleles will be located on homologous chromosomes.
The exchange of genetic material occurs through crossing-over, where segments of DNA from one chromosome are swapped with segments of DNA from the other chromosome. The result of crossing-over is that the daughter cells produced during meiosis have a unique combination of alleles.
This genetic diversity is essential for sexual reproduction, as it allows for offspring to inherit a unique combination of traits from their parents. The role of meiosis in generating genetic diversity is not limited to synapsis and crossing-over.
During meiosis, there is also a process known as independent assortment, where the homologous chromosomes separate randomly into the daughter cells. This means that each daughter cell will receive a random combination of chromosomes from the parent cell.
The combination of independent assortment and crossing-over means that the daughter cells produced during meiosis have a unique combination of alleles that is different from the parent cell. In fact, the number of possible combinations of alleles that can be produced during meiosis is so large that it is virtually impossible for two gametes to be genetically identical.
The genetic diversity produced during meiosis has important evolutionary implications. The diversity allows for natural selection to act on populations, as individuals with beneficial traits are more likely to survive and reproduce.
This means that the genetic makeup of a population can change over time as a result of natural selection, leading to the evolution of new species. The role of meiosis in genetic diversity is not limited to sexual reproduction.
Meiosis also plays a crucial role in the production of haploid cells, which have only one copy of each chromosome.
In some organisms, such as fungi and algae, haploid cells can undergo mitosis to produce multicellular structures. This process is known as alternation of generations, and it is essential for the life cycle of these organisms. {2}
Frequently Asked Questions
Sources
1 – Frontiers in Genetics: “Failure of homologous synapsis and sex-specific reproduction problems.”
2 – Encyclopaedia Britannica: “Alternation of generations | Definition & Examples.”