We explain what sexual reproduction is in biology, its process and how it occurs in animals and humans. Also, asexual reproduction.\
What is sexual reproduction?
In biology , sexual reproduction is any process of generation of a new individual that involves two individuals of the same species but of different sex. It differs from asexual reproduction because it involves the combination of the genetic materials of both parents to form a new one.
Sexual reproduction is characteristic of eukaryotic organisms , that is, of those whose cells have a well-defined nucleus , and especially of multicellular ones.
It occurs according to different mechanisms, which always lead to fertilization: the union of sexual cells from each of the parents, to initiate a process of accelerated multiplication and form a zygote, which will later become an embryo and finally a new individual of the species, ready to join the ecosystem .
The origin of sexual reproduction is a biological mystery, but it is assumed that it arose on our planet 1.2 billion years ago , before the first multicellular organisms existed .
Some theories suggest that it was a consequence of viral infections, others to certain types of cellular phagocytosis that allowed the incorporation of the DNA of the devoured cells into that of the devourer. In any case, it made it possible to combat the genetic impoverishment of communities , and gave way to a genetic variation that did not depend on sporadic mutations .
See also: Plant reproduction
sexual selection
Individuals with attractive features manage to reproduce by sexual selection.
The possibility of sexual reproduction, that is, of the combination of the genetic material of two individuals of the same species to form a new and unique one, led to the appearance of sexual living beings . In other words, sexual dysmorphism arose : the differentiation of individuals based on theirbiological sex (male and female).
Said differentiation is the product of sexual selection: an evolutionary process described by Charles Darwin in his work The Origin of Species (1859), and which supposes the effect of competitive pressure, that is, natural selection , among the individuals of the same species , for agreeing to copulation, that is, for reproducing.
Put more simply: individuals of the same species compete with each other to reproduce efficiently, through different mechanisms that, over time , modified and specialized their own bodies.
Thus, the body of males and females of the different species began to develop physical and biochemical characteristics that allowed them to have access to the sexual act, such as the specialization of certain parts of the body for reproductive purposes, or the development of others to carry out sexual intercourse. courtship and attracting a sexual partner, such as bright colors .
process of sexual reproduction
Reproduction is the meeting between the male and female gametes.
Sexual reproduction can occur according to different mechanisms, but always within a very similar scheme of biochemical and cellular processes, which we can describe as follows:
- Organisms generate sex cells (gametes), which have half the genetic content of an ordinary cell and are specifically designed for reproduction . These cells originate through a process called meiosis , in glands and specialized organs of the body and are different depending on the sex. In the case of animals, these are sperm (male) and ovules (female).
- This is the name given to the encounter between the female and male gametes, to fuse and produce a zygote, that is, a new cell endowed with a unique and unrepeatable genetic material, possessing all the potential to become a complete individual. For said cell to be produced, the gametes must physically unite, which can occur in the environment (external fertilization) or within the female organism (internal fertilization). Depending on this, a sexual intercourse or act must then take place.
- Embryonic development. In this stage the zygote multiples, grows and gains complexity, going through numerous stages until it produces an embryo: a new individual of the species of its parents, which from then on will grow, develop and eventually be ready to start a life of its own. This embryonic development will take place inside the maternal body (in the case of internal fertilization) thus giving rise to pregnancy; or it will take place inside eggs (in the case of external fertilization).
- When embryonic development is complete, the new individual appears into the world for the first time, which implies breaking the egg membrane or being expelled from the maternal body through the birth canal. Thereafter, there will be a new individual of the species in the world.
sexual reproduction in animals
Most reptiles are oviparous.
The vast majority of animals reproduce sexually, so they also present sexual dysmorphism: physical differences between males and females. However, not all reproduce in the same way, since there are:
- Oviparous animals. Those that reproduce sexually, either through intercourse (internal fertilization) or the release of gametes (external fertilization), but always through eggs deposited by the female. These eggs are fertilized inside or outside the female by the male’s sperm and each give rise to a new individual of the species (or several). Examples of oviparous animals are: insects, fish, reptiles and birds.
- Viviparous animals. Those that reproduce sexually and through intercourse, that is, with internal fertilization, for which they go through a gestation or pregnancy, at the end of which the new individuals are expelled alive, already formed, ready to lead an independent life. Examples of viviparous animals are: mammals and humans .
- ovoviviparous animals. Those that reproduce sexually and through intercourse, and through egg laying, but the latter occurs within the mother’s body, from which the formed individuals will later emerge. It is an intermediate option between the two previous ones. Examples of ovoviviparous animals are: sharks, rays and certain types of snakes.
human sexual reproduction
Human beings go through a prolonged pregnancy of 9 months.
Human beings, as mammals, reproduce sexually and through intercourse , with internal fertilization of the female, which then goes through a period of pregnancy or prolonged pregnancy, for approximately 9 months.
During this process, the maternal womb bulges as the zygote becomes an embryo and the latter a fetus, to finally be expelled through the birth canal.
However, unlike other animal species, human beings have a prolonged and vulnerable childhood, especially in the first months of life, since the development of our brain is after childbirth . Otherwise it would be very difficult for the rigid head of a child to pass through the birth canal.
More in: Human reproduction
Asexual reproduction
Asexual reproduction does not require the participation of two sexes or gametes.
Unlike sexual reproduction, asexual reproduction does not require the participation of two sexes, nor gametes, but two offspring can be obtained from a single individual , but with the proviso that they will be genetically identical to the parent , that is, They will be your clones .
Asexual reproduction differs from sexual reproduction in that it is much cheaper in energy terms, and easier in its cellular procedures, but it lacks a fundamental element, which is genetic variability. To do this, the species of living beings that reproduce in this way depend on spontaneous DNA mutations.