INBREEDING

From Big Medical Encyclopedia

INBREEDING (English. inbreeding; in in, inside + breeding cultivation; synonym inbreeding) — crossing or marriage of the individuals consisting among themselves in the close related relations. Form of the closest And. forced self-pollination (autogamy) at plants is. Crossings (marriages) of individuals, the related relations between which are less close, than it is observed on average for populations (see), designate as outbreeding. Kinds of outbreeding are breed crossing, a krossbriding, crossing of inbredny individuals (i.e. the individuals who were born as a result And.) with unrelated to them autbredny individuals, so-called top crossing.

Essence And. is that at inbredny organisms degree of homozygosity (increases see. Mendel laws ) owing to the fact that the probability of receiving by posterity of identical genes considerably increases in marriage of related individuals from both parents. Probability of establishment of homozygosity, i.e. drawing up factor pair of identical alleles (see), depends on the frequency of this allele in population, to a cut individuals belong. Than the low frequency of an allele, subjects is less probability of a meeting of two heterozygous carriers of this allele and subjects less probability that the posterity will inherit these alleles from both parents. In case of related marriages this probability does not depend on the frequency of an allele in population, is a constant for each of degrees of relationship between parents. For some of them it much more exceeds the probability existing for panmiksny population, in a cut the probability of emergence of homozygous carriers is rather small (see. Isolates ). This pattern is especially accurately traced concerning alleles which frequency in population is low.

Increase of degree of homozygosity depends on degree of relationship marrying. E.g., if the individual of parent population in a homozygous state had 50% of genes, then at self-pollination at plants absolute homozygosity will practically be established already to the seventh generation. At marriage of brothers and sisters to the 16th generation absolute homozygosity is reached. Marriage of cousins and cousins to the 16th generation will give only 62% of homozygous genes. It should be noted that relationship of individuals does not matter for the signs linked to a floor at men (see. Inheritance , Paul, genetics of sex ). The signs linked to a floor are defined by the genes localized in gonosomes. At men of steam of gonosomes also Y-hromosomami is presented X-. In this regard the genes defining the signs linked to a gender of men are presented not by a factor pair as it is observed for autosomes (see. Chromosomes ) and gonosomes of the woman (couple of XX), and in a single, gemizigotny state, i.e. they are shown always, and their manifestation cannot be disguised by other allele. Owing to this fact the existing opinion that the hemophilia described in the reigning families of Europe (pathology, development a cut is defined by disturbances in X-chromosome) is result And., has no reasons. The disease of men of hemophilia depends on whether he will receive the struck chromosome from mother, but not from the one who is his father.

Degree of homozygosity, i.e. degree And., determine by the formula offered by S. Wright:

where Fx — coefficient And., n — number of generations from the general ancestor in the area of mother, n1 — number of generations from the general ancestor in the area of the father, ∑ — the standard designation of the sum. Coefficient And. shows not only probability of homozygosity of an individual on this allele, but also the fact that both alleles of this locus are identical on the origin. If the general ancestor in itself already was inbredny, then allowance for an inbrednost of the general parent is entered into a formula (1 + Fa), and the formula takes a form:

In that case when the individual in the family tree has several general ancestors, coefficient And. define by summing of coefficients And. on each general ancestor. It is possible to determine by an indicator of Fx degree And. populations. In this case coefficient And. reflects the frequency of homozygotes in the studied population in comparison with panmiksny population. Coefficient And. is the size of probability and changes ranging from 0 to 1. Fx value = 0 corresponds to a panmixia, a Fx = 1 is an indicator that marriages consisted in the studied family only between relatives.

The number of related marriages in 20 century, especially since its middle, clearly decreases that first of all is caused by disintegration of isolates and the considerable amount of population shift.

And. it is possible to estimate on phenotypical (see. Genotype ) to similarity of individuals of one line. Than it is more at individuals of one line of identical genes, i.e. the izogennost is higher, the more representatives of this line phenotypical are similar among themselves. Degree And. it is possible to establish by efficiency of organ and tissue transplantation: the more between the donor and the recipient of genetic similarity, the effectiveness of transplantation is higher.

In some cases there is necessary an increase in degree of homozygosity of an individual and receiving so-called pure lines of animals. In particular, it concerns to laboratory animals: to mice, rats, hamsters, rabbits and others which are widely used for check of efficiency of various pharmaceuticals, serums and a number of the factors influencing an animal organism up to factors of space flight. For these researches extremely important that they were carried out on objects with the most identical genotype since influence of the studied factor can be darkened by different reaction of various genotypes.

And. played a big role in creation of a number of the best breeds of page - x. animals. However use And. in wide scales leads, as a rule, to a number of negative effects: to decrease in fertility, productivity, weakening of the constitution. Therefore the distribution in livestock production of artificial insemination which repeatedly reduced the number of the used producers creates threat of spontaneous distribution And., and especially among cattle. Though increase in posterity from the best producers is desirable as one of effective methods of increase in productivity of page - x. animals, distribution And. can cause the negative effects much surpassing it positive effects. By the most perspective method of avoidance negative and uses of positive effects And. top crossing (crossing of inbredny producers with is unrelated to them autbredny females).

Question of effects and admissibility And. up to 18 century interested people only concerning their. For a long time at most of the people and tribes of the globe marriages between close relatives like brother — the sister, the father — the daughter, mother — the son, the uncle — the niece, the cousin — the cousin, etc. were considered as harmful and were prohibited, and sometimes were even severely punished. The examples of positive influence given sometimes And. are an exception of the general rule of negative effects of inbredny marriages. Stern (S. of Stern) provides the data of a number of researchers proving that in the USA, France, Japan and Sweden in 20 — is the 50th 20 century old in posterity from marriages of cousins and sisters a mertvorozhdennost, mortality at early age and prevalence physical. and were 1,5 — 3,5 times higher than mental defects, than in posterity from unrelated (autbredny) marriages. N. P. Dubinin gives these researches, carried out in three districts of France in 1956, also shown that in posterity from marriages between relatives on each 1000 newborns it was 39 — 76% more mortinatus and the dead in the early childhood, than in posterity from marriages between the people who were not consisting in relationship.


Bibliography: Darwin H. Change of animals and plants in a house state, the lane with English, page 364, M. — L., 1941; Dubinin N. P. General genetics, M., 1976; Use of inbreeding in livestock production, under the editorship of Ya. L. Glembotsky, M., 1977; Stern K. Fundamentals of genetics of the person, the lane with English, page 359, M., 1965.

Ya. L. Glembotsky.

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