Download Nov8 - Salamander Genome Project

Box 9.1 History of Conservation Genetics
Goals:
(1) Preserved genetic diversity all levels
(2) Promote the continuance of ecological
and evolutionary processes that
foster and sustain biodiversity.
How can Molecular Markers Help Us?
Molecular Markers Can be Used to Estimate Heterozygosity
See Table 9.1 in Avise
Many examples of reduced heterozygosity
Limitations of Molecular Markers:
Are they suited to detect past historical events?
Are they suited to measure genome-wide heterozygosity?
Are they likely to be associated or independent of
phenotypic variation?
8 pops
The frequency
of heterozygotes
decreases under
drift.
Hg+1 = Hg[1-1/2N]
Inbreeding Decreases the Frequency
of Heterozygotes
Gen 3 = 62.5
Gen 2 = 125
Allele frequencies
do not change,
but genotypic freqs
do change.
Heterozygosity and Inbreeding
Heterozygosity in
an inbred population
=
Heterozygosity in a
random mating
population
x
Prob.
not IBD
H F = HO (1 - F)
Anytime F is greater than 0, the frequency of heterozygotes is
Lower in an inbred population than in a random mating population.
Inbreeding coefficient (F) = Probability that two alleles
are identical by descent
What is F for an individual of half sib parents?
AB
0.5
AB
0.5
0.5
0.5
A
A
B
B
0.5
0.5
0.5
0.5
AA
BB
(0.5)4 = 0.0625
(0.5)4 = 0.0625
F = 0.0625 + 0.0625 = 0.125
Does genetic variation always determine the likelihood
of extinction?
1) A number of studies have documented fitness affects
associated with heterozygosity (Avise p. 487).
2) However, non-genetic aspects should also be considered
in the formulation of species management plans.
For example, a species may be endangered because
mating and social behaviors are severely affected.
Also, random changes in population size may be important
irregardless of heterozygosity.
Heterozygosity and Disease Resistance
Cheetah are now genetically impoverished populations,
especially at MHC loci.
Feline infectious peritonitis (FIP) recently swept through
several colonies killing 50-60% of the animals.
However in domestic cats, the average mortality rate is
only 1%.
Also, there is growing evidence that disease is playing
a major role in the current and ongoing world-wide
amphibian declines.
Inbreeding increases
egg failure in Parus major
Can organisms avoid
inbreeding depression?
Mate Choice
Genetic Incompatibility
Dispersal
Inbreeding Depression in Humans
Presumably,
inbreeding reduces
mean fitness by
“revealing” deleterious
recessive alleles.
Prairie Chicken
Migration, Genetic Drift,
Non-random Mating
Prairie chicken
almost went extinct
in the 1950’s.
Why did fitness decrease
after early efforts were
implemented to
conserve remnant
populations?
Average number of DNA alleles per locus
Illinois
pre-bottleneck
5.12
Illinois
present
3.67
Other Pops in
Midwest
5.33-5.88
An Extinction Vortex
Loss of Habitat
Extinction or reduced population sizes
Gene Flow - reduced / eliminated
Genetic Drift and Non-random Mating
Loss of heterozygosity
Deleterious alleles increase in frequency
Inbreeding Depression -- lowered fitness
Extinction or reduced population sizes