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A white Bengal tiger at the Houston Aquarium. Because of the inbreeding and resulting genetic defects the Association of Zoos and Aquariums barred member zoos from breeding white tigers.

Inbreeding is reproduction from the mating between related individuals. Inbreeding is a form of nonrandom mating.[1] A mating between relatives is commonly referred to as consanguineous mating. An inbred line is the result from animals being mated brother to sister, generation after generation.[2] Among humans, excessive inbreeding may be avoided with the help of elaborate cultural traditions[3] and religious principles. However in some cultural traditions, consanguineous marriages are preferred and often prescribed as is the case with some followers of the Dravidian tradition.[4]

Measurements of inbreeding

Inbreeding is measured using the inbreeding coefficient, that can range from 0 to 1, which is a measure of of the probability that two alleles are identical by descent. This coeficient is usually denoted by F.[1] It is defined as the proportionate reduction in the frequency of heterozygous genotypes in a population of inbred organisms (HI) compared with the value (2pq) that would be expected with random mating.[5] This coefficient denotes the fraction by which it is reduced the proportion of heterozygotes expected.[5] The formula is:

F = (2pq - HI)/2pq


F = The inbreeding coefficient.
p = Frequency of the dominant allele.
q = Frequency of the recessive allele.
HI = Frequency of heterozygous genotypes in a population of inbred organisms.

Inbreeding depression

The increasing emergence of lethal and deleterious traits due to inbreeding is called inbreeding depression.[1]


  1. 1.0 1.1 1.2 Pierce, Benjamin A (2008). Genetics: A Conceptual Approach (3rd ed.). New York: W. H. Freeman and Company. p. 687-688. ISBN 978-0-7167-7928-5. 
  2. Snustad, Peter; Simmons, Michael J (2010). Principles of Genetics (5th ed.). River Street, Hoboken, NJ: John Wiley & Sons. p. 80. ISBN 978-0-470-39842-5. 
  3. Brahmachary, R.L.; Sarkar, Mousumi Poddar; Dutta, J (1993). "Evolution of Chemical Signals". In Majumder, Partha P. Human Population Genetics: A Centennial Tribute to J.B.S.Hadane. London: Plenum Press. p. 96. ISBN 0-306-44572-7. 
  4. Malhotra, Kailash C.; Vasulu, T. S (1993). "Structure of Human Populations in India". In Majumder, Partha P. Human Population Genetics: A Centennial Tribute to J.B.S.Hadane. London: Plenum Press. p. 207-233. ISBN 0-306-44572-7. 
  5. 5.0 5.1 Hartl, Daniel L (2011). Essential Genetics: A Genomics Perspective (5th ed.). Sudbury, Massachusetts: Jones and Bartlett Publishers. p. 481. ISBN 978-0-7637-7364-9.