The achievements of population genetics, its massive theoretical justification of all natural processes occurring in natural habitats, allow people to use this knowledge for 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 can a person achieve by using them, we will analyze in this article.
Inbreeding - what is it?
To begin with, let's decide on the concept itself. So, inbreeding, speaking the scientific genetic language, is the concentration of alleles of genes identical in origin in the same genotype, that is, in a particular organism.
If we answer the question “Inbreeding - what is it?” With simpler words, then we can say that this is a targeted crossing of closely related forms of plants, animals, people with the aim of accumulating certain alleles of the gene in the genotype that carry the desired trait. There are actually several synonyms for this process. So, when it comes to the human population, then closely related marriages are called incest. If we are talking about plants, then they talk about incuhta. Inbreeding is a concept for livestock. However, the same term can be used in crop breeding.
Heterosis
There is such a thing as an extreme degree of inbreeding. This happens when:
- the animal is capable of self-fertilization;
- the plant is self-pollinated.
In these cases, it is much easier to accumulate homozygous alleles with the desired trait in generations, because the set of chromosomes from different individuals is excluded. This property is actively used in crop production. Individuals from the first generation with self-pollination often give such results in which the yield increases by 60%! This is called heterosis and is the most used method of obtaining such products of plant origin, such as:
- cotton;
- pepper;
- peas;
- beans;
- citrus;
- wheat;
- barley and others.
Under the conditions of inbreeding carried out by humans, the manifestation of harmful genes can be extinguished by transferring them to a heterozygous state in future generations. This is done by artificial selection. If the plant lives in natural conditions, then this selection is carried out by nature itself, it is natural. That is why in nature among self-pollinating plants it is practically impossible to find deformities, distortions and serious genetic diseases.
The history of the concept
If you plunge into history, then such a thing as incest has existed since antiquity, since the time of the pharaohs. In different civilizations this phenomenon was not equally perceived. For example, among the ancient Romans, incest was considered a terrible sin. But in such places as Egypt, the countries of Europe, pre-Columbian America, and among all adherents of paganism, this process was a completely normal component of life. The brothers freely married their sisters, and this was welcomed because it allowed to preserve the "noble" blood of the dynasty in the case of royal and royal families. However, the Bible forbade such incest, incest was considered a terrible sin, so the whole Christian world stopped such processes over time.
If we talk about plants, animals, then what inbreeding is, what is heterosis, people only learned over time empirically. It is clear that then the knowledge of population genetics was not available. People were guided only by visibility, by experimental tests. However, this was enough to be noticed: to obtain the necessary traits and to fix them in the offspring, closely related forms should be crossed with the existing gene that is externally manifested.
The same was true for plants. It is known that back in the 14th century, beautiful tulips of non-standard colors, obtained by incut, were grown in the Ottoman Empire. Among animals, dogs were especially often inbreed, as 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 most powerful, hardy and trained hunting dogs for the result. True, a large number of individuals arising from mutations were destroyed.
The degree and coefficient of inbreeding
The theoretical substantiation of the concept under consideration was given by many scientists, however, the works of the Englishman Wright and the Russian Kislovsky are most valuable. Together, but independently of each other, they managed to create a formula that allows calculating the inbreeding coefficient in generations. It looks like this:
F x = Ʃ F (1/2) n + ni-1 * (1 + F a ) * 100, where
- F x is the inbreeding coefficient, expressed as a percentage;
- F a - inbreeding rate from a common ancestor;
- n, n i - pedigree lines.
If you know several generations of a species, and also have information about the inbreeding coefficients already calculated for ancestors, then you can calculate the indicator for any organism. It should only be indicated that such calculations are carried out only with a theoretical purpose. Practice shows that this method is inefficient, since it does not take into account recessive alleles carrying harmful mutations. And they can become both homo- and heterozygotes with frequent process steps.
Therefore, the results of practice differ from those calculated theoretically. The Wright-Kislovsky formula is used only when writing graduate theses, dissertations, where a very large amount of data for 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 necessary trait.
Classification
Close (close) inbreeding - what is it? This is one of the varieties of the process, which will be discussed below. Moderate and distant inbreeding is also distinguished. To understand the main differences and similarities between different species, we will consider each of them.
Close inbreeding
This is the most complex and dangerous type of this process. It consists in crossing the closest blood relatives of breeds. If we translate into human degrees of kinship, then this, for example, mother and son, father and daughter, brother and sister.
With this type of crossing, a close exchange of similar alleles occurs. 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 hidden recessive mutant gene, and they will be the greater, the larger the number of offspring. In such cases, the accumulation of harmful signs quickly occurs and deformities appear, there is stillbirth, sterility of organisms.
Moderate view
Such inbreeding of animals consists in the crossing of more distant relatives. Translating into human degrees of kinship, these are, for example, cousins, niece and uncle, and so on.
As a result, it is possible, gradually, by carefully selecting, to achieve homozygosity for the required 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 healthy with almost every litter.
Of course, the recessive allele of the mutant gene will still manifest itself, perhaps more than once, but eventually fades completely, turning into a heterozygous.
Distant view
This inbreeding of animals implies the crossing of not so closely related individuals. So, if you project on people, it can be, for example, second cousins .
A similar process gives a very weak result, often almost imperceptible. In addition, studies have confirmed that over time, generations of individuals with sharply negative traits appear. Animals are more painful, weak, mutant genes prevail and cause deformities.
Obviously, getting the best offspring that can pass on its traits to the next generation and continue to do the chain further is what inbreeding is aimed at (the purpose for which it is used).
Crossbreeding Examples
Inbreeding in livestock has been used for a long time. And it is on the example of representatives of mammals that it is obvious how it works. Speaking about such inbreeding, the following can be examples:
- purebred horse populations;
- clean lines of thoroughbred dogs;
- species uniformity of the necessary cat breeds and so on.
In principle, this crossing can be applied to all species of animals. Just for most it will be a pure experiment. But inbreeding, the 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 intricacies of crossbreeding and getting a truly beautiful and healthy offspring. But genetics is a very capricious science, so misses happen. Recessive genes can prove themselves, and the individual will be unsuitable for sale, for its intended purpose, as a whole for life.
Inbreeding in cynology
As we have already noted, dog handlers are more devoted 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 proved that the moderate effect of such a cross gives the greatest effect.
Conditions for successful inbreeding of dogs:
- genotype quality of the ancestor;
- competent and calculated approach to the process;
- the choice of a moderate option.
The main thing for any dog breeder is to prevent the onset of inbred depression. This is the state of the line when individuals begin to transmit mutant genes to each other, causing deformities. As a result, all individuals are weak, painful, and often die.
Outbreeding
Inbreeding in plant breeding is very important, because many crops are self-pollinated, therefore its effectiveness is high. But if we talk about animals, then more often they use outbreeding, which is the opposite action in structure. That is, non-related individuals cross at all, as a result they get good thoroughbred lines. In this way, horses, cows, pigs, dogs and other domestic animals are bred. Outbreeding is a simple and reliable breeding method, since from generation to generation they receive offspring of stable productivity.