Genetic purging

As Purging (. Engl of to purge: clean, purify ) or inbreeding recovery is referred to in the population genetics of the phenomenon that can occur under certain conditions, despite strong inbreeding in a reduction or even elimination of inbreeding depression in inbred populations. Purging is most often related to a genetic bottleneck and can occur when strong inbreeding in conjunction with a strong selection pressure occurs in a population of fitness. For this, the reproduction rate must be high enough to get under the increased selection at least the minimum viable population size.

• 2.1 Increased inbreeding depression
• 2.2 Partial Purging
• 2.3 Full Purging

Background

Under the inbreeding depression refers to the phenomenon that with increasing inbreeding, a reduction of fitness (fertility, infection resistance, durability, etc.) can be determined. Since inbreeding always leads to an increase in homozygosity, this can only happen if the responsible alleles are at least partly inherited dominant- recessive.

Partial dominance model

The partial dominance model assumes that inbreeding depression arises because recessive alleles are formed with a negative effect on the fitness phenotypically more frequently due to increased homozygosity of the inbred population, as is the case in non- inbred populations. This model is considered today as the most likely.

Overdominance model

The overdominance model assumes that the increased homozygosity is independent of the existing alleles responsible for the loss of fitness. It has so far not be refuted, but is probably considered by most experts to be less than the partial dominance model.

Scenarios

After a genetic bottleneck exists in an inbred population basically three possible scenarios for further development:

Increased inbreeding depression

After the bottleneck, the inbreeding depression increases in the population and remains constant in the sequence at a high level. This can lead to the extinction of the population.

Partial Purging

After the bottleneck increases the inbreeding depression, but goes back in the sequence to a lower value. This value is still higher than in the population before the bottleneck.

Full Purging

After the bottleneck increases the inbreeding depression, but is in the order within a few generations the value of the population before the bottleneck back or even less than this. This happens when the high inbreeding is combined with strong selection on fitness: By selecting the deleterious alleles are removed from the population. Because of inbreeding -related increased homozygosity less alleles survive this selection in its heterozygous form, as is the case in a non- inbred population. This in turn leads to an elimination of inbreeding depression from the population until after hundreds of generations of mutation due back new detrimental recessive alleles accumulate.

Examples of Purging

• Golden hamsters
• Peromyscus polionotus
• Chillingham cattle
• Spekegazellen
• Iceland horses
• Dingo