Reproduction

Reproduction

Reproduction is a biological process that can be sexual or asexual, which allows the formation of new individuals, being a common property of all known forms of life, with the purpose of preserving the species.

Self-perpetuation

 One of the fundamental characteristics of living beings is the ability to reproduce, to generate new living beings with characteristics similar to them.

 The strategies and structures that living beings use to fulfill the reproductive function are diverse. Within this wide range of strategies, it is possible to find sexually reproducing species that produce a huge number of eggs, like most fish, in order to ensure that some reach adults. Other species, such as the albatross or the whale, generate a single offspring for each reproductive stage, which they care for intensely for long periods of time. This reduces the chances of death and increases the chances of continuity of the species.

 In nature, we can find groups of specimens that combine both sexual and asexual reproduction, such is the case of plants, which, in addition to reproducing sexually, reproduce asexually through shoots, creeping stems, underground roots, etc. The reproductive strategies of other organisms include the regeneration of lost body parts, such as starfish and some species of lizards. On the other hand, a large number of species divide asexually countless times, giving rise to a large number of descendants, as is the case of most unicellular organisms.

The reproduction process of living beings is one of their most important characteristics. It creates new organisms, which can replace those that have been damaged or died. There are two basic types:

 Asexual reproduction

 Asexual reproduction is related to the mechanism of mitotic division.[3] It is characterized by the presence of a single parent, which partially or completely divides and gives rise to one or more individuals with identical genetic information.[3]​ This type of reproduction does not involve sexual cells or gametes, and there are almost no differences between parents and their descendants,​ the occasional differences are caused by mutations.

In asexual reproduction, a single organism is capable of giving rise to other new individuals, which are exact copies of the parent from a genetic point of view. A clear example of asexual reproduction is the division of bacteria into two daughter cells, which are genetically identical.[4] In general, it is the formation of a new individual from maternal cells, without meiosis, the formation of gametes. or fertilization. There is, therefore, no exchange of genetic material (DNA). The progenital living being respects the characteristics and qualities of its parents.

 Examples in animals

 Asexual reproduction is found in almost half of the animal phyla. Parthenogenesis occurs in the hammerhead shark and the blacktip shark. In both cases, the sharks had reached sexual maturity in captivity in the absence of males, and in both cases the offspring were shown to be genetically identical to the mothers. The New Mexico whip is another example.

Some reptiles use the ZW sex determination system, which produces males (with ZZ sex chromosomes) or females (with ZW or WW sex chromosomes). Until 2010, the ZW chromosome system used by reptiles was thought to be incapable of producing viable WW offspring, but a female boa constrictor (ZW) was found to have produced viable female offspring with WW chromosomes.[8]​ The female boa could have chosen any number of male partners (and had done so successfully in the past) but on these occasions reproduced asexually, creating 22 female babies with WW sex chromosomes.

 Polyembryony is a widespread form of asexual reproduction in animals, whereby the fertilized egg or a later stage of embryonic development divides to form genetically identical clones. Within animals, this phenomenon has been best studied in parasitic Hymenoptera. In 9-banded armadillos, this process is mandatory and usually results in genetically identical quadruplets. In other mammals, monozygotic twinning has no apparent genetic basis, although its occurrence is common. There are currently at least 10 million identical human twins and triplets in the world.

Bdelloid rotifers reproduce exclusively asexually and all individuals in the class Bdelloidea are female. Asexuality evolved in these animals millions of years ago and has persisted ever since. There is evidence to suggest that asexual reproduction has allowed animals to develop new proteins through the Meselson effect that have allowed them to better survive periods of dehydration.[9] Bdelloid rotifers are extraordinarily resistant to damage from ionizing radiation due to the same DNA-preserving adaptations that are used to survive dormancy.[10]​ These adaptations include an extremely efficient mechanism for repairing DNA double-strand breaks.[11]​ This repair mechanism was studied in two species of Bdelloidea, Adineta vaga, and Philodina roseola[12] and appears to involve mitotic recombination between homologous DNA regions within each species.

 Molecular evidence strongly suggests that several species of the stick insect genus Timema have used only asexual (parthenogenetic) reproduction for millions of years, the longest period known for any insect.

 In the grass thrips genus Aptinothrips there have been several transitions towards asexuality, probably due to different causes.