Achievements population genetics, its massive theoretical foundations of all natural processes occurring in the habitats, allow people to use this knowledge for their own needs.For example, a very common phenomena such as inbreeding and outbreeding.More familiar to all synonymous to these terms - incest.What are these processes from a scientific point of view and what a person can achieve by using them, we explain in this article.
Inbreeding - what is it?
To begin to define the notion.Thus, inbreeding, genetic speaking scientific language, is the concentration of identical by descent alleles consisting of one genotype, ie, a particular organism.
If more than simple words to answer the question "Inbreeding - what is it?", We can say that it is a targeted hybridization of closely related forms of plants, animals, people with the aim of accumulation in the genotype of certain alleles of the gene carrying the desired trait.In fact, there are several synonyms of the process.So, when it comes to the human population, it is closely related marriages is called incest.If you talk about plants, it talk about inbreeding.Inbreeding - concept for livestock.However, this term may used in crop breeding.
There is such a thing as an extreme degree of inbreeding.This occurs when:
- animal is capable of self-fertilization;
- plant is self-pollinated.
In these cases, accumulate in generations homozygous alleles with the correct sign is much easier, in fact excluded from the set of chromosomes of different individuals.This property is widely used in plant breeding.Specimens from the first generation by self-pollination often produce such results in which yield is increased by 60%!This is called heterosis and is the most used way to obtain such plant foods as:
- barley and others.
in terms of inbreeding exercised person may repay proyavlyaemosti harmful gene transfer them to the heterozygous state in future generations.This is accomplished by an artificial selection.If the plant lives in vivo, such a choice is made by nature, it is natural.That is why in nature among self-pollinating plants hardly meets deformities, distortions and serious genetic diseases.
history of the development of the concept
If you dip into history, the notion of incest, there is a very old, from the time of the pharaohs.Different civilizations differently perceived this phenomenon.For example, the ancient Romans incest was considered a terrible sin.But in places like Egypt, European countries, pre-Columbian America, and all followers of paganism, this process was quite normal component of life.Brothers freely married sisters, and this was welcomed, because it allows to preserve the "noble" blood in the case of the royal dynasty and royal families.However, the Bible prohibit the incest, incest was considered a terrible sin, so the whole Christian world stopped in time such processes.
If we talk about the plants, animals, that is, inbreeding, heterosis what people learned only over time by experience.It is understood that while the knowledge of population genetics were not available.People are guided only clarity, experimental tests.However, it was enough to have been seen: to obtain the desired features and fixing them in the offspring should be a cross between closely related forms to the existing gene exhibited by externally.
The same applies to plants.It is known that in the XIV century in the Ottoman Empire were grown beautiful tulips unusual colors obtained by inbreeding.Among the animals most often subjected to inbreeding dogs, since they were the main attribute of the hunt, and she, in turn, - practically the main entertainment.
inbreeding in dogs allowed to obtain the strongest, hardiest and coached the result of hunting dogs.The truth is a large number of individuals, arising from mutations were destroyed.
degree and inbreeding coefficient
Theoretical study of the concept have been given by many scientists, but the most valuable works of the Englishman Wright and Russians Kislovsky.Together, but independently of each other, they have managed to create a formula to calculate the coefficient of inbreeding in generations.It looks as follows:
Fx = Σ 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 - lineages.
If you know several generations of the species, and have information about the already calculated the inbreeding coefficient for the ancestors, it is possible to calculate the rate for any organism.Only it should be noted that these calculations are made only from the theoretical purpose.Practice shows that this method is inefficient, since it ignores the recessive alleles carrying deleterious mutations.And they can be both homo- and heterozygotes at frequent process.
Therefore, results of the practice are different from the calculated theoretically.Formula Wright-Kislovsky used only when writing dissertations, term papers, dissertations, where a very large amount of data for many generations requires systematization and similar payments.
If we talk about the degree of inbreeding, it we have designated above.In the practice of dog breeding is denoted by its Roman numerals, which indicate in which generation had a common ancestor with the correct sign.
The close (close) inbreeding - what is it?This is one form of the process, which will be discussed below.Also allocate moderate and remote inbreeding.To understand the main differences and similarities between different species, look at each of them.
This is the most difficult and dangerous form of the process.He is crossing the closest blood relative breeds.If translated into human-degree relatives, it is, for example, a mother and son, father and daughter, brother and sister.
With such a crossing occurs close exchange of similar alleles.As a result, the desired sign appears quickly in the offspring of the first generation.However, the danger is that forms a special can carry hidden recessive mutant gene and will be greater the larger the number of offspring.In such cases, rapid accumulation of harmful symptoms and deformities appear, there is a stillbirth, infertility organisms.
Such inbreeding animals is crossed more distant relatives.Translated into human degree of kinship, it is, for example, cousins, niece and uncle, and so on.
As a result, you can gradually, making careful selection, to achieve homozygosity for desired option.This process is long, but it minimizes the harmful homozygous alleles.As a result, you can get a good generation, strong, hardy and healthy in almost every litter.
course recessive allele of the mutant gene will still be apparent, perhaps, not once, but over time completely dies out, going to the heterozygotes.
This implies mating inbreeding animals are not so closely related individuals.So, if the project on people, it can be, for example, second cousins and sisters.
This process gives a result very weak, often practically invisible.In addition, studies have confirmed that with the passage of time there are generations of individuals with sharply negative signs.Animals more painful, weak, mutant genes predominate and cause deformities.
obvious that getting the best offspring, able to transmit their characteristics to the next generation and continue to do so on up the chain - is something that is directed inbreeding (the purpose for which it is used).
Inbreeding in livestock used for a long time.And it is an example of representatives of mammals clearly how it works.Talking about such inbreeding, examples include:
- thoroughbred horse population;
- clean lines of purebred dogs;
- species monotony relevant breeds and so on.
In principle, you can use a crossover to all kinds of animals.Just for most it is a pure experiment.But inbreeding, examples of which we have given above - this is a task of great practical value.
Especially great merit belongs to the experienced dog breeders who know the ins and outs of crossing and getting a truly beautiful and healthy offspring.But genetics - the science is very capricious, so blunders occur.Recessive genes can express themselves, and especially to be unsuitable for sale for the intended purpose, the whole of life.
Inbreeding in cynology
As we have noted, dog privy to the secrets of the phenomenon more than any other professionals.Inbreeding dogs - an important condition for the breeding of purebred lines.Experienced dog breeders proved that the greatest effect gives it a mild form of such crossing.
Conditions for successful inbreeding dogs:
- quality genotype ancestor;
- competent and a calculated approach to the process;
- choice moderate option.
main thing for any breeder - to prevent the beginning of inbreeding depression.It is a state of the line when individuals begin to communicate with each other mutant genes that cause deformities.As a result, individuals are weak, painful, and often die.
Inbreeding in plant breeding is very important, because many crops samoopylyaemy, so its efficiency is high.But when it comes to animals, often used yet outbreeding - the opposite effect on the structure.That is crossed generally unrelated individuals to afford good thoroughbred line.In this way bred horses, cows, pigs, dogs and other pets.Outbreeding - a simple and reliable method of breeding, as from generation to generation is obtained by stable productivity descendants.