Diversity within species Flashcards
(10 cards)
Why is it important to conserve genetic diversity?
As species diversity declines, so too does genetic diversity, which itself is positively related to the fitness of individuals and the viability of populations. Conserving genetic diversity means that populations have a greater potential to evolve, and so are more resistant to environmental perturbation.
At which three levels does genetic diversity occur at within species?
1) Within individuals: different genes can have different levels of allelic richness (number of potential forms) and heterozygosity (likeliness of being different forms in the individual’s genome).
2) Between individuals, within populations: different individuals will carry a different array of alleles and different rates of heterozygosity.
3) Between populations: different populations may have genetic characteristics that differentiate them from other populations.
What three properties can be used as estimates of genetic diversity?
1) Polymorphism (the proportion of genes that have more than one possible allele, and the most common allele has a frequency of less than 95% (otherwise monomorphic)).
2) Heterozygosity (either the proportion of genes at which the average individual is heterozygous, or the proportion of individuals that are heterozygous for a particular gene).
3) Allelic richness (the number of different alleles in the species / population / individual).
What is genetic drift?
Genetic drift is a process through which allele frequency randomly changes over generations due to the “sampling error” of the individuals that happen to breed. The chance increases in smaller populations and there is a risk of fixation, where one allele becomes completely dominant (100% of the diversity). The expected rate of change of heterozygosity over ‘t’ generations is H(t) = H0[1-(1/2N)]^t
What is a population bottleneck?
A population bottleneck occurs when a population recovers after being small and fixation plus a reduced gene pool leads to alleles being lost. While heterozygosity can recover, allelic richness cannot apart from through a very slow process of mutation. The population becomes genetically simplified.
What are founder effects?
Founder effects happen when a new population is started / founded from a sample of individuals and their alleles. If a small number of individuals founded the new population, only a small sample of alleles from the original population may be selected and genetic diversity can decline further by genetic drift. This may explain the relationship between propagule pressure and non-native species invasion success.
What can be the effects at the individual level of low genetic diversity?
Individuals that are subject to low genetic diversity may have reduced fitness, for example if deleterious alleles have increased in frequency following a bottleneck and therefore homozygotes for these alleles will increase in frequency (and so are expressed as harmful traits). Furthermore, genes associated with disease resistance often have many alleles at several loci, so heterozygous individuals may be more resistant to disease.
What can be the effects at the population level of low genetic diversity?
Low genetic diversity reduces the potential of the population to adapt to environmental changes via evolution. Inbreeding can also reduce viability of the offspring. Both factors lead to high death rates during environmental changes.
What is inbreeding depression and when does it occur?
Inbreeding depression is when reduced genetic diversity leads to reduced fitness of offspring. It is most common in small populations e.g. in zoos, but can also happen if close relatives breed in larger populations.
What is outbreeding depression and when does it occur?
Outbreeding depression is when an individual breeding with another from a different population leads to a reduced fitness of offspring. It is most common in amphibians, where local populations may be highly adapted to local conditions with adaptive gene combinations that can be broken up during outbreeding.
