- What is parthenogenesis?
- Causes of parthenogenesis
- Types of parthenogenesis
- Examples of parthenogenesis
We explain what parthenogenesis is, its causes, types and examples of species that use this form of reproduction.
What is parthenogenesis?
Parthenogenesis is a mechanism of reproduction which consists of the development of unfertilized female sex cells, that is, of ovules that segment themselves until they form a complete embryo, endowed with the same genetic material from his parent.
Parthenogenesis is therefore a form of asexual reproduction that does not bring genetic variety to the species, but instead creates genetic copies (clones) of the mother, since only the females of certain species are capable of this type of reproduction.
Hence its name comes from the Greek words parthenos, "Virgin" and genesis, "Generation", since it does not require the intervention of a male, although in some cases copulation is required.
However, this process can only occur in species capable of reproducing sexually, since it requires the creation of female gametes.
The descendants obtained by parthenogenesis are often called parthenotes and they can be haploid (n) or diploid (2n), depending on the species.
For example, in the community of the bees, the males or drones are obtained in this way. They are usually haploid, since their only role in the community is to fertilize the egg-laying queen, while the female workers are all diploid, obtained from fertilized eggs.
Causes of parthenogenesis
Parthenogenesis can occur in some species depending on environmental situations, as a way to increase the number of individuals community, and face adverse conditions, waiting for a more conducive scenario to resume sexual reproduction.
At the same time, the origin of this ability in different types of living creatures it is an evolutionary mystery. It is known, for example, that bacteria of the order Rickettsiales (such as Wolbachia) are capable of infecting different arthropods nematodes and induce parthenogenesis.
This reproductive mechanism is known to be common in reptiles, insects, amphibians, and some species of fish and birds. In the mammals rarely occurs, except by hand-induced artificial techniques human.
Types of parthenogenesis
There are two types of parthenogenesis, depending on whether or not there is a process of meiosis in the production of the new individual, that is, depending on whether it has one or two chains of DNA in their chromosomes:
- Ameiotic or diploid parthenogenesis. The egg is divided by mitosis and not meiosis, so the resulting individual is diploid. It can be considered a type of asexual reproduction, and is common in flatworms, rotifers, crustaceans, insects and amphibians.
- Meiotic or haploid parthenogenesis. The ovum divides by meiosis, without being fertilized, so the resulting individual can be haploid (a single DNA strand on the chromosome) or can regain its diploid condition, duplicating the information genetics inherited from the mother. It is common in annelids, rotifers, flatworms, fish, amphibians, reptiles, and insects.
Examples of parthenogenesis
The hammerhead shark reproduces by parthenogenesis when there is a shortage of males.
Some examples of species capable of doing parthenogenesis are:
- In bees and ants, as well as in other hymenopteran insects, males are created by parthenogenesis and females by fertilized eggs.
- Aphids and other species of insects parasites of the plants can reproduce by parthenogenesis when there is an abundance of food, thus enlarging the colony; otherwise, they go exclusively to sexual reproduction, to obtain males and females.
- The so-called "hammerhead shark" (Sphyrna mokarran) and some other species of tropical fish are capable of reproducing through parthenogenesis when there is a shortage of fertilizing males.
- Parthenogenesis is very common in certain species of geckos, snakes and monitor lizards, especially the so-called "Komodo dragons" (Varanus komodoensis).