Transcript Inbreeding - People Server at UNCW

Inbreeding
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Calculating inbreeding coefficients
from pedigrees
half-sib mating
F = probability of [(a) or (b)] = 1/16 + 1/16 = 1/8
Outbred population
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Inbred population
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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
Inbreeding depression in
captive mammal populations
Inbreeding depression in
humans
Inbreeding depression in plants
is common
from Futuyma (1998), p. 313
In experimental studies of plants, inbreeding
depression is widespread. It is also the likely
cause of lower fitness in small and endangered
plant populations.
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
from Futuyma (1998), p. 312
Inbreeding depression in Parus major
van Noordwijk and Scharloo (1981)
Failure of egg hatching
increased with the
inbreeding coefficient of
parents
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
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
Genetic restoration of greater
prairie chickens
• males display on communal breeding sites
known as leks
• the species depends on intact grassland
habitat for survival
Number of males displaying on leks
Prairie chickens in Illinois were nearly
extinct by 1994. Birds were introduced
from Nebraska, Kansas, and Minnesota.
Prior to introduction, there was a
continuous decline in hatching
success. Immediately after the
introduction, hatching success
improved.
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