What is microevolution?
the change in allele frequencies in populations over generations
What is a gene?
consists of two alleles in diploid individuals
(more accurately, genetic locus)
What are alleles?
different forms of a gene corresponding to different DNA sequences in each form
- one allele per chromosome, and one chromosome from each parent
What is a phenotype?
a product of inherited genotype and environmental influences
What is a mutation?
changes in an individual’s DNA sequence
- mutations occur randomly and create new alleles
- mutations can have no effect (no change in phenotype) or can have a large effect (lethal)
What are mutations caused by?
- errors in DNA replication (small-scale or chromosomal)
- structural damage to DNA
What is whole-genome duplication?
it’s an important driver of evolution by supplying genetic material and increasing genome complexity
What are the two sources of genetic variation?
- Mutations
- sexual reproduction
What three factors alter allele frequencies in populations?
Natural selection, genetic drift, and gene flow
What causes adaptive evolution?
natural selection.
non adaptive evolution: any change in allele frequency that does not lead to a population to become more adapted to its environment.
What causes non-adaptive gene flow?
Genetic drift & gene flow.
- their effect on allele frequencies is primarily random.
What is directional selection?
favors individuals differ from the current mean phenotype of a population in one direction.
- a population’s genetic variance shifts toward a new phenotype with higher relative fitness
What is relative fitness?
the contribution an individual makes to the gene pool of the next generation, relative to the contributions of others
What is disruptive selection?
favours individuals at both extremes of the phenotypic range
- average phenotypes are less fit than either extreme phenotype, and maintains genetic variation in the population
what is stabilizing selection?
favours intermediate or common traits by selecting against extreme phenotypes.
- the mean of the population stays the same, but the genetic variation in the population decreases.
- very common, removes individuals with lower fitness
What is genetic drift?
- random changes in allele frequency in a population
- genetic drift is more likely in small populations
- rare alleles are more likely to be lost due to genetic drift
- reduces genetic variation in a population through loss of alleles
- creates evolutionary change, but is non-adaptive
What is the bottleneck effect?
a sudden reduction in population size due to a change in the environment (within its natural range)
- allele frequency in the next generation is different than the previous generation. If the population is small, it may be further affected by genetic drift
What is the founder effect?
occurs when a few individuals become isolated from a larger population
- the founding population has a small fraction of the total gene pool in the original population.
What are the effects of genetic drift?
- has the largest impact on small populations
- causes allele frequencies to change at random
- can lead to loss of genetic variation within populations
- can cause harmful alleles to become fixed in small populations
What is gene flow?
the movement of alleles between populations of a species
- different from the founder effect, it can introduce new variation into the receiving population
- gene flow reduces variation between populations over time
What are the three factors that alter allele frequencies in populations and bring about most evolutionary change?
- natural selection (adaptive)
- genetic drift (non-adaptive)
- gene flow (non-adaptive)
What is neutral variation?
genetic variation that does not confer a selective advantage or disadvantage
- natural selection does not affect the frequency of neutral mutations
what is balancing selection?
occurs when natural selection maintains stable frequencies of multiple alleles in the gene pool of the population
What is heterozygote advantage?
occurs when an organism in two different alleles of a particular gene (heterozygote) has greater fitness than an organism with two identical copies of either allele (homozygote)
