Achievements of population genetics, its massive theoretical substantiation of all natural processes occurring in habitats, allow people to use this knowledge in their own needs. So, phenomena such as inbreeding and outbreeding are very common. A more familiar synonymous concept for these terms is incest. What are these processes from a scientific point of view and what a person can achieve using them, we will analyze in this article.
Inbreeding - what is it?
To begin with, let's define the concept itself. So, inbreeding, speaking in scientific genetic language, is the concentration of gene alleles identical in origin in one genotype, that is, in a particular organism.
If you answer the question "Inbreeding - what is it?" in simpler words, then we can say that this is a purposeful crossing of closely related forms of plants, animals, people with the goal ofaccumulation in the genotype of certain alleles of the gene that carry the desired trait. In fact, there are several synonyms for this process. So, when it comes to the human population, closely related marriages are called incest. If we are talking about plants, then they talk about incubation. Inbreeding is a concept for animal husbandry. However, the same term can also be used in crop breeding.
Heterosis
There is such a thing as the extreme degree of inbreeding. This happens when:
- animal is capable of self-fertilization;
- the plant self-pollinates.
In these cases, it is much easier to accumulate homozygous alleles with the desired trait in generations, because a set of chromosomes from different individuals is excluded. This property is actively used in crop production. Individuals from the first generation when self-pollinated often give results in which the yield increases by 60%! This is called heterosis and is the most common way to obtain plant products such as:
- cotton;
- pepper;
- peas;
- beans;
- citrus;
- wheat;
- barley and others.
Under the conditions of inbreeding carried out by man, it is possible to extinguish the manifestation of harmful genes by transferring them to a heterozygous state in future generations. This is done through artificial selection. If the plant lives in natural conditions, then such selection is carried out by nature itself, it is natural. That is why in nature among self-pollinatingplants are almost impossible to meet deformities, distortions and serious genetic diseases.
History of the development of the concept
If you plunge into history, then such a thing as incest has existed since antiquity, since the time of the pharaohs. This phenomenon was perceived differently in different civilizations. For example, among the ancient Romans, incest was considered a terrible sin. But in places like Egypt, the countries of Europe, pre-Columbian America, and for all adherents of paganism, this process was a completely normal component of life. Brothers freely married sisters, and this was welcomed, as it allowed the "noble" blood of the dynasty to be preserved in the case of royal and royal families. However, the Bible forbade such incest, incest was considered a terrible sin, so the entire Christian world stopped such processes over time.
If we talk about plants, animals, then what is inbreeding, what is heterosis, people learned only over time empirically. It is clear that at that time the knowledge of population genetics was not available. People were guided only by visibility, experimental tests. However, this was enough to be noticed: in order to obtain the desired traits and fix them in the offspring, closely related forms with an existing gene that is manifested externally should be crossed.
The same applied to plants. It is known that as early as the 14th century, beautiful tulips of non-standard colors were grown in the Ottoman Empire, obtained by incubation. Among animals, the most frequently subjecteddog inbreeding, since they were the main attribute of hunting, and she, in turn, was practically the main entertainment.
Inbreeding in dogs made it possible to obtain the strongest, most enduring and best-trained hunting dogs. True, a large number of individuals that arose from mutations were destroyed.
Degree and coefficient of inbreeding
Theoretical substantiations of the concept under consideration were given by many scientists, but the most valuable are the works of the Englishman Wright and the Russian Kislovsky. Together, but independently of each other, they managed to create a formula that allows you to calculate the inbreeding coefficient in generations. It looks like this:
Fx=Ʃ F(1/2)n+ni-1 (1 + Fa) 100, where
- Fx - inbreeding coefficient expressed as a percentage;
- Fa - inbreeding coefficient from a common ancestor;
- n, ni - pedigree lines.
If you know several generations of a species, and also have information about the inbreeding coefficients already calculated for the ancestors, then you can calculate the indicator for any organism. It should only be pointed out that such calculations are made only for theoretical purposes. Practice shows that this method is inefficient, since it does not take into account recessive alleles that carry harmful mutations. And they can become both homo- and heterozygotes if the process is carried out frequently.
Therefore, the results of practice differ from those calculated theoretically. The Wright-Kislovsky formula is used only when writing theses, term papers, dissertations, where a very large amount of data over many generations requires systematization and similar calculations.
If we talk about the degree of inbreeding, then we have already indicated it above. In the practice of dog breeding, it is customary to designate it with Roman numerals, which show in which generation there was a common ancestor with the desired trait.
Classification
Close (close) inbreeding - what is it? This is one of the varieties of the process, which will be discussed below. There are also moderate and distant inbreeding. To understand the main differences and similarities between different species, let's look at each of them.
Close inbreeding
This is the most difficult and dangerous type of this process. It consists in crossing the most closely related breeds by blood. If translated into human degrees of kinship, then this is, for example, mother and son, father and daughter, brother and sister.
With this type of crossing, there is a close exchange of similar alleles. As a result, the desired trait quickly manifests itself in the offspring of the first generation. However, this is dangerous because the resulting individual can carry a latent recessive mutant gene, and there will be more of them, the larger the number of offspring. In such cases, the accumulation of harmful signs quickly occurs and deformities appear, stillbirth, infertility of organisms occurs.
Moderate view
Such inbreeding of animals is the crossing of more distant relatives. Translating into human degrees of relationship, these are, for example, cousins \u200b\u200band sister, niece and uncle, and so on.
As a result, you can gradually, making a careful selection, to achieve homozygosity for the desired parameters. This process is long, but it minimizes the homozygosity of harmful alleles. As a result, you can get a good generation, strong, hardy and he althy with almost every offspring.
Of course, the recessive allele of the mutant gene will still manifest itself, perhaps more than once, but over time it will fade completely, turning into a heterozygote.
Distant view
This inbreeding of animals involves the crossing of not so closely related individuals. So, if projected onto people, it could be, for example, second cousins.
Such a process gives a very weak result, often almost imperceptible. In addition, studies have confirmed that over time, generations of individuals with sharply negative signs appear. Animals more sickly, weaker, mutant genes predominate and cause deformities.
Obviously, getting the best offspring that can pass on their traits to the next generation and continue to do so down the chain is what inbreeding is aimed at (the purpose for which it is used).
Crossing examples
Inbreeding has been used in animal husbandry for a long time. And it is on the example of representatives of mammals that it is obvious how it works. Speaking of such inbreeding, examples include the following:
- Purebred horse populations;
- pure lines of purebred dogs;
- species uniformity of desired cat breeds and so on.
In principle, such crossbreeding can be applied to all kinds of animals. It will just be purely experimental for most people. But inbreeding, examples of which we have given above, is already a task of serious practical importance.
Especially great merit belongs to experienced dog breeders who know all the subtleties of crossing and getting a truly beautiful and he althy offspring. But genetics is a very capricious science, so mistakes happen. Recessive genes can show up and make the individual unfit for sale, for its intended purpose, for life in general.
Inbreeding in cynology
As we have already noted, cynologists are more privy to the secrets of the phenomenon under consideration than all other specialists. Inbreeding in dogs is an important condition for breeding purebred lines. Experienced dog breeders have proven that it is the moderate form of such crossing that gives the greatest effect.
Conditions for successful inbreeding of dogs:
- quality of the ancestor genotype;
- competent and calculated approach to the process;
- choosing a moderate option.
The main thing for any dog breeder is to prevent the onset of inbreeding depression. This is such a state of the line when individuals begin to transfer mutant genes to each other that cause deformities. As a result, all individuals are weak, sickly and often die.
Outbreeding
Inbreeding is very important in plant breeding, because many crops are self-pollinating, so its efficiency is high. But if we talk about animals, then outbreeding is still used more often - an action that is opposite in structure. That is, non-related individuals are crossed at all, as a result, good thoroughbred lines are obtained. Horses, cows, pigs, dogs and other domestic animals are bred in this way. Outbreeding is a simple and reliable breeding method, as from generation to generation, stable offspring are obtained in terms of productivity.
