Conservation genetics:

 Conservation genetics:

Conservation genetics is an interdisciplinary subfield of Population Genetics that aims to understand the dynamics of genes in populations principally to avoid extinction.

Therefore, it applies genetic methods to the conservation and restoration of biodiversity.  researchers involved in conservation genetics come from a variety of fields including population genetics, molecular ecology, biology, evolutionary biology, and systematics. Genetic diversity is one of the three fundamental levels of biodiversity,

so it is directly important in conservation. Genetic variability influences both the health and long-term survival of populations because decreased genetic diversity has been associated with reduced fitness, such as high juvenile mortality, diminished population growth, reduced immunity, and ultimately, higher extinction risk.

Contents

 1 Genetic diversity

 2 Importance of genetic diversity

 3 Contributors to extinction

 4 Techniques

 5 Applications

 6 Implications

 

Genetic diversity:

Genetic diversity is the variability of genes in a species. A number of means can express the level of genetic diversity: observed heterozygosity, expected heterozygosity, the mean number of alleles per locus, or the percentage of polymorphic loci.

Importance of genetic diversity:

Genetic diversity determines the potential fitness of a population and ultimately its long-term persistence, because genes encode phenotypic information. Extinction risk has been associated with low genetic diversity and several researchers have documented reduced fitness in populations with low genetic diversity. For example, low heterozigosity has been associated with low juvenile survival, reduced population growth, low body size, and diminished adult lifespan.

Heterozygosity, a fundamental measurement of genetic diversity in population genetics, plays an important role in determining the chance of a population surviving environmental change, novel pathogens not previously encountered, as well as the average fitness of a population over successive generations. Heterozygosity is also deeply connected, in population genetics theory, to population size (which itself clearly has a fundamental importance to conservation). All things being equal, small

populations will be less heterozygous - across their whole genomes - than comparable, but larger, populations. This lower heterozygosity (i.e. low genetic diversity) renders small populations more susceptible to the challenges mentioned above.

In a small population, over successive generations and without gene flow, the probability of mating with close relatives becomes very high, leading to inbreeding depression - a reduction in fitness of the population. The reduced fitness of the offspring of closely-related individuals is fundamentally tied to the concept of heterozygosity, as the offspring of these kinds of pairings are, by necessity, less heterozygous (more homozygous) across their whole genomes than outbred individuals. A diploid individual with the same maternal and paternal grandfather, for example, will have a much higher chance of being homozygous at any loci inherited from the paternal copies of each of their parents' genomes than would an individual with unrelated maternal and paternal grandfathers (each diploid individual inherits one copy of their genome from their mother and one from their father).

High homozygosity (low heterozygosity) reduces fitness because it exposes the phenotypic effects of recessive alleles at homozygous sites. Selection can favour the maintenance of alleles which reduce the fitness of homozygotes, the textbook example being the sickle-cell beta-globin allele, which is maintained at high frequencies in populations where malaria is endemic due to the highly adaptive heterozygous phenotype (resistance to the malarial parasite, Plasmodium falciparum).

Low genetic diversity also reduces the opportunities for chromosomal crossover during meiosis to create new combinations of alleles on chromosomes, effectively increasing the average length of unrecombined tracts of chromosomes inherited from parents. This in turn reduces the efficacy of selection, across successive generations, to remove fitness-reducing alleles and promote fitness-enhancing allelels from a population. (A simple hypothetical example would be two adjacent genes - A and B - on the same chromosome in an individual. If the allele at A promotes fitness "one point", while the allele at B reduces fitness "one point", but the two genes are inherited together, then selection can't favour the allele at A while penalising the allele at B – the fitness balance is "zero points". Recombination can swap out alternative alleles at A and B, allowing selection to promote the optimal alleles to the optimal frequencies in the population - but only if there are alternative alleles to choose between!)

The fundamental connection between genetic diversity and population size in population genetics theory can be clearly seen in the classic population genetics measure of genetic diversity, the Watterson estimator, in which genetic diversity is measured as a function of effective population size and mutation rate. Given the relationship between population size, mutation rate, and genetic diversity, it is clearly important to recognise populations at risk of losing genetic diversity before problems arise as a result of the loss of that genetic diversity. Once lost, genetic diversity can only be restored by mutation and gene flow. If a species is already on the brink of extinction there will likely be no populations to use to restore diversity by gene flow, and any given population will (by  definition) be small and therefore diversity will accumulate in that population by mutation much more slowly than it would in a comparable, but bigger, population (since there are fewer individuals whose genomes are mutating in a smaller population than a bigger population).