PARASEXUAL REPRODUCTION: MONERAS, PROTISTS AND FUNGI - BIOLOGY - 2025

The parasexual reproduction is a special type of reproduction that involves the transfer of genetic material without a process of reduction division (meiosis) or gamete intervention occurs. Parasexuality was discovered in 1956 by the Italian geneticist Guido Pontecorvo.

The parasexual cycle is a mitotic mechanism to achieve the production of offspring with new genotypes through genome recombination. Unlike sexual reproduction, it is a process that lacks coordination and does not involve meiotic cell divisions.

Candida albicans parasexual cycle. Taken and edited from: Anja Forche, Kevin Alby, Dana Schaefer, Alexander D Johnson, Judith Berman, Richard J Bennett.

Although it was originally discovered in fungi, later this type of reproduction has also been observed in other organisms, such as bacteria and protists. Some authors have even suggested the existence of parasexuality in flowering plants.

In mushrooms

Parasexual reproduction was originally discovered in the fungus Aspergillus nidulans, although its capacity has already been demonstrated in a large group of different species. The cycle consists of three stages: diploidization, mitotic chiasm formation, and haploidization.

Diploidization

The process of parasexual reproduction in fungi begins, as in the case of the sexual cycle, with the formation of a heterokaryote by the union of two genetically different mycelia and fusion of their cellular cytoplasms (plasmogamy). The resulting heterokaryote has cells with two haploid nuclei.

Occasionally, the haploid nuclei can fuse (karyogamy), producing diploid nuclei. These nuclei can divide by mitosis giving rise to new diploid nuclei. In this way, the heterokaryote will have cells with haploid nuclei and with diploid nuclei.

Mitotic chiasm formation and crossover

The chiasm is a bridge that is established between sister chromatids during the recombination that occurs in the meiotic process. During mitosis, although much less frequently, the formation of this bridge between chromatids can also occur.

The rare occurrence of the mitotic chiasm is because the chromosomes in this type of cell division generally do not pair in a regular arrangement. However, it occurs in the parasexual cycle, resulting in genetic recombination that results in variations in the progeny.

Haploidization

Haploidization is the process by which a cell with a chromosomal load greater than the normal haploid load of the species, recovers the haploid condition by eliminating chromosomes, without a meiosis process occurring.

During the mitotic divisions of the diploid nuclei of the parasexual cycle, nondisjunction of chromosomes can occur, causing one of the resulting nuclei to have an additional chromosome and the other a missing chromosome. These nuclei are called aneuploids.

These aneuploid nuclei tend to be unstable and lose chromosomes during subsequent mitotic divisions, until the haploid chromosome load is reached.

In Monera

In the classification systems of Copeland, 1938, and Whittaker, of 1969, Monera is a kingdom of unicellular organisms that are characterized by lacking a nucleus. It corresponds to the now called Eubacteria and Archea, as well as the ancient Prokaryotes.

In these organisms, parasexual reproduction has been signaled according to three different mechanisms: conjugation, transformation and transduction.

Bacterial conjugation

It is a process of transfer of genetic material between two bacteria (or archaea), one that acts as a donor of said material and the other as a recipient. This transfer occurs by direct contact between both cells.

The transferred genetic information, generally a plasmid or a transposon, allows the donor cell to share with the recipient a certain characteristic or advantage that the latter lacks, such as resistance to antibiotics. If both cells have this characteristic, then the conjugation will not take place.

Transformation

It is the modification of the genetic material of a prokaryotic cell due to the incorporation into its genome of genetic material that is found naked in the environment and that penetrates its cell membrane. This genetic material is known by the name of exogenous DNA.

Not all bacteria are capable of incorporating exogenous genetic material, those that can do so are said to be in a state of competition, which can occur both naturally and artificially.

Transduction

It consists of the transfer of genetic material from one bacterium to another due to the action of a bacteriophage or phage virus. Bacteriophages replicate inside bacterial cells, taking advantage of the processes of replication, transcription and also of their translation.

During the encapsulation of the genetic material of the phage, part of the genetic material of the bacterium can be trapped, which can later be transported and transferred to other bacteria, after the phage is released from the donor bacteria.

Bacterial transduction. Taken and edited from: Microbiology (Odontology) subject at the University of Oviedo (Spain).

In protists

Protists are a polyphyletic group of organisms that are characterized by not developing from embryonic leaves or laminae. Most of these organisms are unicellular, however, they can also be multicellular.

It has recently been discovered that some species in this group can reproduce parasexually. Researchers have shown that plasmogamy can occur in these organisms, for example in amoebae of the genera Cochliopodium and Variosea, while they are cultured under laboratory conditions.

After plasmogamy, karyogamy occurs, with a mixture of the genetic material from each nucleus and then nuclear fission and plasmotomy, releasing daughter cells with genetic information different from that of the parents, due to the interbreeding process.

Applications

In mushrooms

Researchers have used parasexual reproduction primarily to produce new strains of asexual fungi that are of some commercial importance. For example, to produce hybrids capable of obtaining better yields in the production of antibiotics.

In Monera

Bacterial conjugation has been used in genetic engineering to transfer genetic material to organisms of different kingdoms. Indeed, in laboratory tests, researchers have successfully transferred genetic material to yeast, plants, mitochondria, and mammalian cells.

This tool has certain advantages over other means of transferring genetic material, such as the fact that it produces less damage to the cell membrane of the recipient cell, as well as the ability to transfer relatively large amounts of genetic material.

In Protista

The recent discovery of the existence of this type of process in protists is the possible cause that no application to it has yet been developed.

References

1. Parasexual cycle. On Wikipedia. Recovered from: en.wikipedia.org.
2. Y. Teklea, OR Anderson & AF Leckya (2014). Evidence of Parasexual Activity in Asexual Amoebae ”Cochliopodium spp. 4 (Amoebozoa): Extensive Cellular and Nuclear Fusion. Protist.
3. Parasexual reproduction process in bacteria. Recovered from: wikiteka.com.
4. AJ Clutterbuck (1996). Parasexual recombination in fungi. Journal of Genetics.
5. Prokaryotic conjugation. On Wikipedia. Recovered from: es.wikipedia.org.
6. Transduction (genetics). On Wikipedia. Recovered from: es.wikipedia.org.
7. Transformation (genetics). On Wikipedia. Recovered from: es.wikipedia.org.