The artificial selection It is a process of genetic change that is carried out by intentionally choosing specific phenotypes, both from animal and plant species. It is used to obtain organisms with defined characteristics, almost always chosen a priori: that is, in advance.
Artificial selection is, therefore, the human choice or creation of the best phenotypes by indirect selection of the genotypes that define it. Examples are dog breeds, cow breeds, corn varieties, or cat breeds.
The first cases of artificial selection in the history of humanity sought a specific objective, but the process was not intentional as in our times, in which man has dedicated himself to the domestication of plants and animals..
In the initial domestication of the dog, for example, selection was applied for traits of interest such as docility. However, at that time the rationale for cross-breeding was not known, and individuals with the desired trait were simply selected; in other words, a posteriori.
After thousands of years of artificial selection, we obtained the modern dog from its common ancestor with the wolf (which is not a domesticated animal).
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Artificial selection by design (conscious) follows a series of specific steps: the first of them is the choice of the desired character or characters.
The second step involves the specific analysis of the heritability of the trait (the heritability of a trait is the role that genetics plays in the transmission or not of a particular trait).
If we place a white flower, for example, in water with blue ink, it will be colored blue, but the heritability of such a character will be null (zero). That is, the flower is not genetically destined to be blue, but white, that is, it was made blue by imposition environmental.
The easiest traits to artificially select are those that are determined by few genes with high heritability values..
Once these two steps have been completed, then the individuals who possess the genes (and respective alleles) of interest are chosen. With these parents we proceed to make the crosses that show the desired trait in the progeny.
This is the most important part of the artificial breeding and selection process, as it involves choosing the appropriate heritable information. Afterwards, we proceed with the crosses and with the application of a selection scheme that allows choosing the appropriate individuals to the objective of the person who directs the selection..
On many occasions, but not always, the stability of the desired trait is sought by making the necessary crosses until the homozygotes of the desired trait are obtained (organisms with two identical alleles for the same gene, dominant or recessive)..
An organism homozygous for a character is a pure line organism, that is, it does not segregate: it always gives rise to the same.
There are many types of traditional artificial selection schemes, as well as more modern ones that involve complex technologies. In traditional artificial selection you can proceed in two ways:
On the other hand, artificial selection is not only achieved thanks to the choice of the organisms that present a certain characteristic (positive selection; only the desired organisms reproduce), but sometimes it is also possible to proceed to the elimination of the individuals lack the character (negative selection; reproduction of unwanted ones is prevented).
Finally, they can be considered as artificial selection methods to the transgenesis and the gene editing. These methods impose heritable changes that cannot be observed naturally. These changes always obey a design and are, therefore, methods of conscious artificial selection.
Through artificial selection, the general health of plants and animals can be improved, but also their productivity and behavior. The latter has led to unethical systems of exploitation of farm animals and pets..
The improvement of plants and animals through traditional and technological means has made it possible to obtain organisms that could hardly have appeared spontaneously. In contrast, it is unlikely that these organisms can survive the living conditions of their wild ancestors (if they still exist)..
Artificial selection has made it possible to increase the more pronounced manifestation of certain characters, but sometimes to the detriment of others. Many consumers complain, for example, of the continuous loss of taste and smell of some vegetables and flowers, which have been improved to extend their life time or resistance to pests..
Finally, artificial selection, based on the choice of few phenotypic variants, reduces the genetic base of the species, which also represents a great disadvantage.
By artificial selection exerted on various species, human beings have managed to achieve, for example:
- All breeds of dogs (Canis lupus familiaris) current
- Hens (Gallus gallus) layers of up to 320 eggs per year
- Cows (Bos taurus) producing more than 20 liters of milk per day
- The phenotypic "variants" cauliflower, Brussels sprouts, cabbage, kale and collard greens, of the unique species of wild mustard Brassica oleracea
- Transgenic papaya plants (Carica papaya) resistant to Papaya ringspot virus.
- Gluten-free transgenic wheat plants
- Various vegetables with longer shelf life
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