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Inbreeding

Inbreeding. A 1 A 1. A 1 A 2. A 2 A 2. A 1 A 1. A 2 A 2. A 1 A 2. A 1 A 1. A 2 A 2. A 1 A 2. A 1 A 1. A 2 A 2. A 1 A 2. Calculating inbreeding coefficients from pedigrees. half-sib mating. F = probability of [(a) or (b)] = 1/16 + 1/16 = 1/8. Outbred population. *. *. *. X. *.

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Inbreeding

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  1. Inbreeding

  2. A1A1 A1A2 A2A2 A1A1 A2A2 A1A2 A1A1 A2A2 A1A2 A1A1 A2A2 A1A2

  3. Calculating inbreeding coefficients from pedigrees half-sib mating F = probability of [(a) or (b)] = 1/16 + 1/16 = 1/8

  4. Outbred population * * * X * * * * * * * * * * * * * * * * * * * * * * * * Inbred population * * * X * * * * * * * * * * * * * * * * * * * * * * *

  5. Consequences of inbreeding • inbreeding “exposes” deleterious recessive genes by making them homozygous • it causes a drop in fitness known as inbreeding depression inbreeding depression = decline in fitness (survivorship, reproductive success) due to mating with relatives

  6. Inbreeding depression in captive mammal populations

  7. Inbreeding depression in humans

  8. Inbreeding depression in plants is common from Futuyma (1998), p. 313

  9. In experimental studies of plants, inbreeding depression is widespread. It is also the likely cause of lower fitness in small and endangered plant populations.

  10. Classic studies of inbreeding in natural populations • van Noordwijk and Scharloo (1981) studied inbreeding in an island population of great tits (Parus major) in Holland • a small isolated population: • pedigree for entire population was determined by banding birds • inbreeding was common

  11. from Futuyma (1998), p. 312

  12. Inbreeding depression in Parus major van Noordwijk and Scharloo (1981) Failure of egg hatching increased with the inbreeding coefficient of parents

  13. However... • while hatching failure increased with inbreeding, hatchlings that did survive showed even higher success when they bred • over several generations, a similar effect may “purge” the genome of deleterious genes

  14. Implications for conservation • inbreeding depression can be severe and its onset can be rapid • endangered populations with a “history” of inbreeding may actually show fewer effects • but, the immediate effects to an historically outbred population could drive it to extinction

  15. Genetic restoration of greater prairie chickens • males display on communal breeding sites known as leks • the species depends on intact grassland habitat for survival

  16. Number of males displaying on leks Prairie chickens in Illinois were nearly extinct by 1994. Birds were introduced from Nebraska, Kansas, and Minnesota.

  17. Prior to introduction, there was a continuous decline in hatching success. Immediately after the introduction, hatching success improved.

  18. Genetic restoration probably lowered inbreeding depression • assays of highly polymorphic microsatellite DNAs showed Illinois populations to be inbred prior to the introduction • this supports the inbreeding depression hypothesis for decline and recovery

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