Topic 7 Flashcards
Population in terms of evolution
the smallest unit of evolutionary change
Microevolution
change in allele frequencies in populations over generations
Gene or Genetic Locus
consists of two alleles in diploid individuals
Gene Pool
All the available alleles present in all individuals in the population
4 Sources of Genetic Variation
Mutations, genetic drift, gene flow, and selection
Mutations
changes in an individual’s DNA sequence that can occur randomly and can create new alleles
Chromosomal mutations
mutations of alleles/chromosomes that can be potentially harmful by deleting, disrupting, or rearranging many loci
Adaptive Evolution
Where a population becomes more adapted to its environment through natural selection
Non-adaptive Evolution
Any change in allele frequency that does not lead a population to become more adapted to its environment caused by random genetic drift and gene flow
3 Modes of natural selection
Directional selectiong
Disruptive selection
Stabilizing selection
Directional selection
Natural selection that favours individuals that 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
Disruptive Selection
Natural selection that favours individuals at both extremes of the phenotypic range. Ex) beak size for different functions of a large beak size and a tiny beak size in the species
Stabilizing Selection
Natural selection that favours intermediate or common phenotypes by selecting against extreme phenotypes that deviate from the current population mean. It results in little or no evolutionary change in a population
Genetic drift
Random changes in allele frequencies in a population that is more likely to occur in small populations and more likely to lose rare alleles.
DOES NOT CREAT ADAPTATIONS
Bottleneck Effect
Genetic drift with a sudden reduction in a population size due to a change in the environment where the allele frequency in the next generation would become different from the previous generation.
4 Effects of Genetic Drift
- largest impact on small populations
- causes allele frequencies to change at random
- can lead to a loss of genetic variation within populations
- can cause harmful alleles to become fixed in small populations
Neutral Variation
Genetic variation that does not confer a selective advantage or disadvantage
Balancing Selection
A form of natural selection that maintains genetic diversity by favouring stable frequencies of multiple alleles in the gene pool of a population
3 Mechanisms of Balancing Selection
- Temporal or spatial variation
- Heterozygote advantage
- Frequency-dependent selection
Frequency-dependent Selection
The fitness of an allele depends on its frequency in the population, usually resulting from interactions between species (predation, parasitism, or competition)
