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Encyclopedia of Genetics, Genomics, Proteomics and Informatics

pp 691-692

# Fixation Index

The fixation index is the average coefficient of inbreeding in a population. In case of random mating, the probability that an offspring would have exactly the same two ancestral alleles at a locus is (1/2)N, where N is the number of diploid individuals in the population. The probability of having two different alleles at the same locus is 1 ā (1/2)N. The coefficient of inbreeding of the first generation of this population is also (1/2)N by definition of inbreeding. In each succeeding generation, the non-inbred part of the population will have a chance to produce offspring with an allele pair identical by descent. Therefore, the coefficient of inbreeding in the next generations will be (1/2)N + [(1 ā (1/2)N] x F, where F is the inbreeding coefficient of the preceding generation. After the gth generation the coefficient of inbreeding of this population will be: F_{g} = (1/2)N + [1 ā (1/2)N]F_{gā1} and this is called the *index of fixation*. Its complement is the *panmictic index* (P_{g}) that repres ...

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- Title
- Fixation Index
- Reference Work Title
- Encyclopedia of Genetics, Genomics, Proteomics and Informatics
- Pages
- pp 691-692
- Copyright
- 2008
- DOI
- 10.1007/978-1-4020-6754-9_6023
- Print ISBN
- 978-1-4020-6753-2
- Online ISBN
- 978-1-4020-6754-9
- Publisher
- Springer Netherlands
- Copyright Holder
- Springer Science+Business Media
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