ch 21: Natural Selection Flashcards
Microevolution
Change in allele frequencies of a population over Generations (small scale)
Sources of new alleles (allows evolution to occur)
- Mutations
- point and chromosomal - Sexual Recombination
- Crossing over, ind assorting, and fertilization
Population Genetics
Study of how population genetics change over time
Population
A group of individuals of the same species that live in the same area an interbreed (offspring must be fertile)
Gene Pool
all alleles for all genes for all members of a population (variation in the population)
Allele Frequency
the frequency at which an allele exists in a population
Fixed Allele
when all members are homozygous for the same allele
The Hardy-Weinberg Theorem
explains how allele frequencies (genotypes) change over time
Hardy-Weinberg Equilibrium
a tool to measure change, Hardy-Weinberg equilibrium describes the constant frequency of alleles in such a gene pool
5 conditions for non-evolving populations are rarely met in nature
- Extremely large population size
- No gene flow
- No mutations
- Random mating
- No natural selection
Events that alter a population’s genetic composition
Natural Selection
Genetic Drift
Gene Flow
Natural Selection
differential selection
Genetic Drift
(unpredictable fluctuations in allelic frequency from one generation to the next) Chance, random, nonadaptive, small pop = greater impact of allele change
2 types of genetic drift
population bottleneck
The Founder Effect
population bottleneck
the seals((big populations to little populations to big populations)
The Founder Effect
splitter groups that separate from the larger, main group may or may not represent the larger group
Gene Flow
introductions of new variations through immigration and emigration
Natural Selection as a Mechanism of Evolution
relative fitness
Acts on Phenotype
relative fitness
contribution an organism makes to the gene pool of next-generation relative to other members. Not size or strength, but only reproductive success
Acts on Phenotype (indirectly on genotype) Changes heritable traits in 3 ways
- Directional Selection- Favors individuals at one extreme of a
phenotypic range - Disruptive Selection- Individuals on both extremes are favored
- Stabilizing Selection- Acts against both extremes phenotypes
individuals in the middle are favored
The Preservation of Genetic Variation(5)
Diploidy Balancing Selection Heterozygote advantage Frequency-Dependent Selection Neutral Variation
Diploidy
recessives are hidden (heterozygosity)
Balancing Selection
natural selection maintains two stable frequencies of two or more phenotypes in a population
Heterozygote advantage
those that are heterozygous at a particular gene locus have greater fitness than those that are not, specific disease
Frequency-Dependent Selection
the fitness of anyone morph declines if it becomes too common in the population.
Neutral Variation
when genetic variation has little or no impact on reproductive success, just a change
3 types of selection(3)
- sexual dimophism
- Intrasexual selection
- Intersexual selection
Sexual dimorphism
phenotypic differences in secondary sex characteristics between the sexes.
Intrasexual selection
mating selection/competition within the same sex
Intersexual selection
mate choice. Female selecting male
Why natural selection cannot produce perfect organisms
- Selection can only edit existing variations.
- Evolution is limited by historical constraints.
- Adaptations are often compromised.
- Chance, natural selection, and the environment interact.
