01 Population Evolution Flashcards
endemic (ecology)
Endemism is the ecological state of a species being unique to a defined geographic location, such as an island, nation, country or other defined zone, or habitat type; organisms that are indigenous to a place are not endemic to it if they are also found elsewhere. The extreme opposite of endemism is cosmopolitan distribution.
evolution
change (in a population) over time
what changes first, the phenotype or the genotype
genotype
list Darwin’s three main postulates
- Genetic variation exists in a population.
- Survival is not random. Those individuals whose characteristics fit them best to their environment are likely to leave more offspring. Overproduction of offspring leads to a struggle for existence where only some of the offspring survive.
- The unequal ability of individuals to survive and reproduce will lead to changes in a population, with favorable characteristics accumulating overtime.
microevolution
change within a species over time
macroevolution
the development of new species
population
a group of the same species living in the same place at the same time
species
a group of individuals that can interbreed and produce fertile offspring (individuals whose genes are capable of being pooled together… see what I did there?)
population genetics
field of study that investigates how populations change genetically over time
what two fields of study does population genetics join?
Darwin’s evolutionary principles with Mendel’s genetics
list the criteria required for a population to be in Harvey-Weinberg equilibrium
- Large population
- Isolated population (no immigration)
- No mutations
- Random mating (no sexual selection)
- No natural selective pressures - all individuals are equal in survival and reproductive success.
what is said of a population that meets all criteria of the Harvey-Weinberg principle?
it is at genetic equilibrium
what are the methods of sexual recombination?
crossing over, independent assortment and random fusion of gametes (fertilisation)
what does sexual recombination do to allele frequency within a population?
nothing, sexual recombination does not change allele frequency. on the other hand, sexual selection does affect allele frequency, as it is a selective pressure.
what is the purpose of sexual recombination?
while sexual recombination does not change overall allele frequency within a gene pool, it does produce great levels of variation at the individual level for selective pressures to operate upon.
list the processes that change allele frequencies
- random mutation
- natural selection (including sexual selection)
- genetic drift
- gene flow
mutations in which cells are most significant to evolutionary processes?
mutations in gametes, as these will be passed down to the next generation
explain why mutations that have large impacts on the phenotype are rare
because of DNA repair mechanisms, the redundant nature of the genetic code (silent mutations), the likelihood of a mutation showing up in protein coding regions of DNA, etc.
what are the classes of mutations?
- lethal: mutations that lead to the loss of alleles from a population, so they are never part of the gene pool
- neutral: mutations that do not benefit or harm the individual and do not aid in either survival or reproductive success of members of a population
- beneficial: mutations that lead to the survival and enhanced reproductive success of an individual (and thus the mutated allele)
what happens to mutations as environments change?
they may turn from neutral to beneficial, or beneficial to lethal, etc.
natural selection
the only mechanism that drives adaptive evolution - a process by which selection of certain phenotypes in a population allows some alleles in the gene pool to persist better than others, called adaptations. natural pressures are placed on the population causing some alleles to be lost and others to be favoured.
directional selection
one extreme is favored while the other is eliminated
adaptive evolution
a process by which selection of certain phenotypes in a population allows some alleles in the gene pool to persist better than others, called adaptations. natural pressures are placed on the population causing some alleles to be lost and others to be favoured.
stabilising selection
pressures are placed on both extremes of a population and the average is favoured
disruptive selection
where the pressures are placed on the average and the extremes are favoured
sexual selection
a subcategory of natural selection specific to reproductive success as it involves obtaining mates for sexual reproduction
intrasexual selection
sexual selective pressures exhibited within a sex (ex. males fighting amongst themselves for mating access)
intersexual selection
sexual selective pressures exhibited between sexes (ex. females choosing a male to mate with, which will pass that males genotype on instead of the less favoured male)
sexual dimorphism
Sexual dimorphism is a phenotypic difference between males and females of the same species. The prototypical example is for differences in characteristics of reproductive organs. Other possible examples are for secondary sex characteristics, body size, physical strength and morphology, ornamentation, behavior and other bodily traits. Traits such as ornamentation and breeding behavior found in one sex only imply sexual selection.
genetic drift
Genetic drift or allelic drift is the change in the frequency of a gene variant (allele) in a population due to random sampling. The alleles in the offspring are a sample of those in the parents, and chance has a role in determining whether a given individual survives and reproduces. A population’s allele frequency is the fraction of the copies of one gene that share a particular form. Genetic drift may cause gene variants to disappear completely and thereby reduce genetic variation.
compare the effects of genetic drift between large and small populations
In large populations, the loss of a small number of individuals and their alleles will not have a large impact. The larger population will buffer their loss. However, genetic drift (random change in alleles) can have a significant impact on smaller populations.
bottleneck effect
A larger population goes through a severe reduction in size due to a natural disaster or intense selective pressure. After bottleneck events take place the alleles represented in the gene pool may change in different directions. The alleles may be overrepresented, underrepresented, or completely lost.
founder’s effect
The founder’s effect occurs when a few individuals become isolated from a larger population. The effects are similar to a bottleneck in that allele frequencies in the small founder population can be different from those in the larger parent population. Some alleles overrepresented, some underrepresented and some lost.
gene flow
In population genetics, gene flow is the transfer of alleles or genes from one population to another. Maintained gene flow between two populations can also lead to a combination of the two gene pools, reducing the genetic variation between the two groups. It is for this reason that gene flow strongly acts against speciation, by recombining the gene pools of the groups, and thus, repairing the developing differences in genetic variation that would have led to full speciation and creation of daughter species.
list and describe the processes that change allele frequencies
- Mutations which randomly contribute new alleles into a gene pool.
- Natural selection which is not random, but adaptive through the selection of alleles for survival and reproductive success. (Sexual selection which is a subcategory of natural selection that is more specific to reproductive success of individuals through mating selection.)
- Genetic drift causes the random drift of alleles due to chance events. This is more enhanced through bottlenecking and the founder’s effect.
- Gene flow contributes to changes in allele frequencies through the movement or migration of alleles in and out of a population.
