Migration

Migration is a process during which the gene pool of a population can be enriched or depleted by new alleles. The spread of these alleles depends on many factors, but to a large extent on natural selection, which is able to eliminate those types of alleles that do not withstand the selection pressure. Migration can greatly limit genetic drift in a population (the change in the frequency of alleles in a population) and is the most important parameter of gene flow (the transfer of genes between populations). Migration can be classified in many different ways, and it depends very much on the field in which we operate.

In sociology, migration, together with birth and death rates, is a key element in the process of population development and significantly influences social and cultural changes of the population at all levels. With economic development, the intensity of migration continues to increase. In this field, the breakdown is as follows:


 * 1) permanent – irreversible migration, moving.
 * 2) short-term – commuting to work, to schools, to services, to recreation; does not require a permanent change of residence.

Division of migration by motive:


 * 1) economical
 * 2) political
 * 3) religious

Further divisions:


 * 1) domestic,
 * 2) interstate (emigration, immigration),


 * 1) voluntary
 * 2) forced.

In zoology, it is perceived as the resettlement of individuals or the entire population to another territory. The breakdown is as follows:


 * 1) regular – e.g., seasonal migrations of birds
 * 2) irregular – e.g., abandonment of areas due to overpopulation and subsequent lack of food

In parasitology, the term migration is used in connection with the transfer of the developmental stage of the parasite.

= Gene flow =


 * in contrast to random changes in gene frequencies in small populations, which are the result of gene drift (random change in gene frequency in small populations), a smooth change in gene frequency arises in large populations due to gene drift
 * a typical example is the steady decline in the frequency of the D allele of the ABO blood group system from approximately 0.3 in East Asia to 0.6 in Western Europe
 * another example is the inflow of "white" genes into the gene pool of American blacks

Example

 * considerable b has been described in the frequency of one of the alleles of the Rh system
 * the frequency of this allele in black Africans is 0.63, and in whites 0.03
 * a frequency of 0.45 was found in blacks in America