lecture 17 Flashcards
(38 cards)
conservation genetics
aims to maintain as much genetic variation as possible so that evolutionary and ecological processes may be allowed to continue.
genetic diversity is functional in conservation:
- correlated with short-term fitness.
- correlated with long-term evolutionary potential.
the goal is to:
protect diversity, adaptive potential, and evolutionary heritage.
solutions:
manage wild populations, reintroductions, captive breeding, and habitat corridors.
processes that shape genetic variation in natural populations:
mutation, selection, migration, and genetic drift.
small populations lead to loss of
genetic diversity and extinction.
polymorphism
frequency of loci with > 1 allele.
- if 2 out of 4 loci are polymorphic, then P=0.5.
allelic diversity
average number of alleles per locus, averaged over all loci sampled.
- (2+4+1+1)/4 = 2.0
observed heterozygosity
frequency of heterozygote individuals per locus, averaged over number of loci sampled.
- (0.2+0.4+0.0+0.0)/4 = 0.6/4 = 0.15
expected heterozygosity
can calculate the expected heterozygosity under HWE. - for a locus with 2 alleles: > heterozygosity (Hexp) = 2pq > homozygosity (Fexp) = 1-2pq > Fexp = p^2 + q^2 - for a locus with > 2 alleles: > Fexp = sum of p^2 with p = frequency of allele i and n = number of alleles. > Hexp = 1-Fexp > Hexp = 1 - sum of p^2
census population size versus effective population size:
- N = census population size; number of individuals in a population.
- Ne = effective population size; size the population contributing offspring to the next generation.
Ne/N ranges from
- 02 to 0.4 with a mean of 0.1
- interpretation - about 10% of individuals contribute to genetic changes.
in an ideal population, N = Ne
- sex ratio 1:1
- random family size
- random mating
- constant size through time
- non-overlapping generations
Effect of sex ration on Ne
Ne = 4 NmNp / (Nm + Np)
effect of family size on Ne
- variation in family size when some pairs have 0 or few offspring, and others have many offspring.
- decrease in Ne as variance in family sizes increases above 2.
- Ne = (4N-2)/(Vk + 2) where Vk = variance in family size.
polygynous
lower Ne
monogamous
higher Ne
effect of cluctuating population size on Ne:
- Ne = t / sum of (1 / Ne) where t = number of generations and Ne = effective size for generation i.
- population bottlenecks:
> census size (N) will recover much faster than Ne.
> the longer the bottleneck, the more variation lost.
genetic drift is the
dominant evolutionary force in small populations and selection in small populations becomes ineffective.
- s = selection coefficients.
solutions to managing small Ne:
captive breeding, reintroductions, wild population management, and habitat corridors.
methods for surveying genetic variation:
- allozymes (1960s): measure genetic variation within and between species.
- mitochondrial DNA (1980s): male vs. female gene flow; identify evolutionary significant units (ESUs).
- microsatellites (1990s): bottlenecks; effective population size; assignment tests.
- SNPs (2000s): identify genomic regions under selection.
allozyme
allelic forms at the same protein-coding locus detected with electrophoresis. protein variants from allelic variants will have slightly different electrical charges, and can be visualized using electrophoresis.
allozyme advantages
codominant markers (both alleles are expressed); easy to replicate; no genetic information about the species necessary (just need some tissues).
allozyme disadvanges
few loci; laborious; several steps removed from the genome (DNA –> mRNA –> 1º –> 2º –> 3º enzyme)
