Understanding the Coefficient of Inbreeding in Population Genetics

The Coefficient of Inbreeding, formulated by Sewall Wright, measures the probability that two alleles at any locus in an individual are identical by descent from the common ancestors of the parents. This is a fundamental concept in population genetics and is often used in animal breeding to measure the level of inbreeding.

In simpler terms, it calculates the chances that an animal’s parents have passed on the same gene variants (alleles) because they both inherited them from a common ancestor. A high COI could indicate a high degree of inbreeding, which might increase the likelihood of an animal inheriting undesirable or harmful traits that are associated with those alleles.

COI is represented as a percentage. The higher the COI, the greater the degree of inbreeding. For example, mating between full siblings (with the same mother and father) would result in offspring with a COI of 25%, indicating that there is a 25% chance that any given gene will be homozygous by descent.

However, it’s worth noting that the Coefficient of Inbreeding is a statistical measure and doesn’t guarantee the presence or absence of any specific gene. It also doesn’t reflect the overall genetic diversity of the population that the individual comes from, which could also be important for its health and viability.

The COI is just one tool in the genetic toolbox that breeders and geneticists can use to assess the health and diversity of a population, and it’s always best used in combination with other information.

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Tony Bierman, "Understanding the Coefficient of Inbreeding in Population Genetics," OBTESA, Accessed June 18, 2024, http://esbt.us/gs.