What is the danger of closely related crosses?

Inbreeding – closely related crossbreeding, crossbreeding of organisms having common ancestors. The common origin of crossed organisms increases the likelihood that they have the same alleles of any genes, so the likelihood of the appearance of homozygous organisms increases with an increase in the degree of kinship. The greatest degree of inbreeding. achieved by self-pollination in plants and self-fertilization in animals. Since a high degree of inbreeding often leads in practice to the appearance of organisms with various hereditary anomalies, in breeding in order to preserve alleles valuable to the host for a breed or variety. point of view, moderate inbreeding is used. The adverse effects of inbreeding to a high degree serve as a genetic justification for the undesirability of closely related marriages in humans. Inbreeding is used to identify recessive alleles, to obtain organisms (clean lines) homozygous for many alleles, to preserve alleles in populations (breeds, varieties) that determine the presence of certain characters. In plant breeding, the term “incuht” is used.
One of the important consequences of inbreeding is the increased incidence of harmful recessive alleles. Typically, such alleles are in the population in a heterozygous state and their manifestation is suppressed by the normal dominant allele. The transition of harmful alleles to a homozygous state impairs the fitness of the offspring, reduces its fertility, vitality and resistance to disease. There is a degeneration of the offspring, or inbred depression. However, inbred depression does not occur in natural populations of self-pollinating plants, despite a high degree of homozygosity: natural selection discards harmful recessive alleles as they transition to a homozygous state.
In breeding, to create breeds and varieties in which economically valuable traits are maximally expressed, an artificial selection of the best parents is carried out in each generation. At the same time, in order to obtain homogeneous lines of organisms with stable desirable characteristics, homozygosity is systematically increased by inbreeding. To avoid its harmful effects, organisms from different (independent) inbred lines are crossed. Thus, it is possible to maintain homozygosity according to the desired characteristics, and to convert harmful alleles into a heterozygous state. In addition, in this way, the opposite effect of inbred depression is obtained – heterosis, which is widely used in breeding.