In general, reproduction can be divided into two types: sexual and asexual. Reproduction is one of the general characteristics of living beings. It is fundamental for the preservation of the species, but it is not necessary for the survival of the individual.
At the molecular level, reproduction is related to the unique ability of DNA to duplicate itself in a semi-conservative way, allowing the resulting cells to have copies of the original DNA molecules.
Reproduction is one of the functions of the human being, perhaps the most important. It is responsible for the continuation of the human race on the planet, “continuation” that bears the name of descendants. But reproduction is not exclusive to human beings, this phenomenon of life occurs in all species of living beings, since the continuity of life is necessary.
However, as no living being is the same – as biology shows – it is common for the types of reproduction to differentiate them as well. Some means of reproduction are simpler and even “fast”, while others are more complex and time-consuming. From protozoa and bacteria to humans, they all reproduce, but how?
The two forms of reproduction of life
Living beings present various types of reproduction, which can be grouped into two major categories, when viruses are not considered: asexual and sexual reproduction. Viruses are separate cases.
The human being performs the type of sexual reproduction (Photo: depositphotos)
- Asexual reproduction:also called vegetative reproduction, in this, living beings have the ability to reproduce by themselves , without the help of another of the same species. There is no genetic combination, since there is no contact between two of the same species. This type of reproduction has several means, which will be addressed later. Individuals who emerge through asexual reproduction are genetically identical to each other. They are, therefore, clones of the initial individual. The descendants will only have different genetic heritage if they undergo mutations, that is, changes in the sequence of nitrogenous bases in some DNA molecule, or changes in the number and shape of chromosomes. Asexual reproduction is simpler, fasterand energetically less expensive. Several are the groups of living beings that reproduce asexually and several are the types of asexual reproduction
- Sexual reproduction:nothing more than the opposite of asexual reproduction. There is a genetic combination – since this reproduction covers fertilization or fertilization (the most common form of sexual reproduction) – and for this reason, it is considered more important in terms of evolution, as it allows the variability of living It is the means of reproduction of the human being, so we are an extremely diverse race. Although it seems simple, it also has several means of occurrence. In sexual reproduction, two specialized haploid cells (gametes) or two special haploid nuclei fuse, forming an egg cell or diploid zygote. By successive mitoses the zygote gives rise to a new individual.
Yes, there are only two types of reproduction of living things. However, there are bryophytes , pteridophytes and celenterates, which reproduce in a curious way called metagenesis or alternation of generations . This reproduction has two phases, the asexual phase and the sexual phase. That is, these species unite the two types of reproduction.
In plants , there are several forms of asexual reproduction. A well-studied case is that of potato . You may have noticed that this type of potato has what is popularly called eyes. In reality, they are gems, structures formed by undifferentiated cells capable of intense mitotic division and that can originate a new plant.
In animals, male gametes are much smaller than female gametes and in most cases, their morphology is related to displacement: they have a hydrodynamic shape, with a long tail used in propulsion. The female gametes of animals are generally large, immobile cells, which contain a reserve of nutrients for the development of the embryo. These nutrients make up the calf.
Because there is a mixture of genetic material, the individuals resulting from fertilization are not the same as their parents, but similar to them. Furthermore, they are not the same, except in cases of identical twins. The sexed mode of reproduction, although more energetically expensive than asexual reproduction, has evolutionary advantages and is the most widely spread among the different groups of eukaryotes.
The environment and reproduction
If the environment were completely stable, without undergoing changes over time and space, asexual reproduction would be very advantageous, as it would preserve the characteristics of the organisms for a given ecological condition. This, however, is not the reality. The environment can always change and an unfavorable change can eliminate the entire population at once if it is formed by genetically identical individuals.
In populations where there is sexual reproduction, this process should not occur, as the genetic variability between individuals is greater. The environmental change can affect part of the population, but another part survives thanks to variations in the genetic material that provide conditions for survival.
Types of asexual and sexual reproduction
- Binary division, bipartition or cissiparity:in this division, organism 1 divides (half and half) and each half of it regenerates, thus forming two descendants. In prokaryotes there is only asexual reproduction and the most common form is bipartition ( bi = two), a name that describes exactly what is happening, from an initial cell, two smaller ones appear, one the same size as the other. This process is also called cissiparity ( scissus = separated, split; paresis= reproduce, give birth) or binary division. Bipartition occurs in prokaryotes without involving mitosis. The terms bipartition, cissiparity and binary division cited for prokaryotes can be applied to asexual reproduction in single-celled eukaryotes, but in these cases there is mitosis
- Gemulation, gemiparity or budding:when buds or buds appear in the organism (on the very surface) that will form new organisms, detaching or not from the one that originated it. Single-celled eukaryotes have this type of asexual reproduction, a process in which the initial individual produces a genetically identical bud. The sprout grows and usually stands out, having an independent life. The term budding is also applied to cases of asexual reproduction in multicellular eukaryotes. This is the case, for example, in hydra , a small animal that lives in fresh water
- Sporulation:spores (which are asexual reproductive cells) are responsible for originating new organisms
- Parthenogenesis:when an egg is not fertilized and there is still an embryonic development that will later originate a new individual.
- Fertilization or fertilization: themost common form of sexual reproduction, consists of the fusion of the male and female gametes, forming the zygote. Whether it is external or internal, this means of reproduction is the most common. The human species performs this type of reproduction.