Evolution By Means Of Natural Selection Flashcards
Natural Selection Requires:
-variation in individuals
-variation is heritable
-more offspring produced than can survive
-some individuals are better at surviving and/or reproduction than others
Darwin identified 4 conditions necessary for natural selection to operate:
- There’s a variation in the traits of individuals within a population.
- The variation in these traits is heritable, so they can be passed from parents to offspring.
- More offspring are produced than can survive (because the environment has limited resources).
- Some individuals are better adapted for survival and reproduction in their environment than others (based on differences in their traits).
Competition between members of the SAME species.
Intraspecific Competition
Competition against other species.
Interspecific Competition
The big-picture idea that species diversify over long periods, eventually forming clusters of closely related groups.
Can lead to speciation.
Macroevolution
Formation of a new species.
Speciation
More concerned with eh details of how evolution occurs. —> Focusing on changes in allele frequencies within shorter periods
Microevolution
Studies the prevalence of alleles in a population and how populations differ genetically.
Population Genetics
An individual gene controls one trait.
1 gene, 1 trait
Single-Gene Trait
Many genes acting together to produce a single trait.
many genes, 1 trait
Polygenic Trait
When a single gene influences more than 1 trait.
Pleiotrophy
Single-gene trait
Natural selection increases the frequency of an allele in a population when the allele codes for an adaptive trait and causes maladaptive alleles to decrease in frequency (or even disappear).
The fitness of a phenotype depends on its relative frequency within a population.
Frequency-Dependent Selection
Single-gene trait
Rare phenotypes have an advantage and natural selection makes them more common.
Negative Frequency-Dependent Selection
Single-gene trait
Adaptive advantage over homozygous.
Sometimes, having copes of different alleles make a heterozygous individual more fit than either homozygous individual.
Heterozygote Advantage
Natural selection affects/influences polygenic traits in 3 ways:
-Directional Selection
-Stabilizing Selection
-Disruptive Selection
How natural selection affects polygenic traits
Favors and extreme phenotype (so the population average shifts to the left OR to the right).
1 extreme, direction shift (1 way).
Directional Selection
How natural selection affects polygenic traits
Favors intermediate phenotypes (narrowing the distribution along the bell curve).
Average phenotype is preferred.
Tightening distribution.
Stabilizing Selection
How natural selection affects polygenic traits
Favors 2+ phenotypes while the average is unfavorable.
More significant changes can be seen within the species. —> Can lead to the evolution of different morphs, subspecies, and even new species.
Favors extreme but NOT intermediate, separate morphs evolve.
Disruptive Selection
A random change in allele frequencies over time.
More likely to affect smaller populations because they have less genetic variation.
Genetic Drift
Genetic drift in larger populations can occur if the population size is dramatically reduced. —> In this case, any surviving individuals have a disproportionately high contribution to the gene frequencies within their dependents.
Population Bottleneck
A type of population bottleneck that occurs when only a few individuals form a new population in an isolated area. —> This isolated population contains only a small amount of genetic variation from the original population.
New species can arise if a population is reproductively isolated.
Founder Effect
p^2 + 2pq + q^2 = 1
p + q = 1
p = homozygous dominant
pq = heterozygous
q = homozygous recessive
Hardy-Weinberg Equation
Applies to populations at equilibrium that aren’t evolving. —> Explained how allele frequencies remained constant over time.
States that allele frequencies in a population remain constant over time if 5 conditions are met: there are no mutations, population size is large and not affected by genetic drift, population is isolated (no gene flow), mating occurs randomly, and natural selection isn’t occurring.
Assumptions of this area rarely met…
Hardy-Weinberg Principle/Law
Genetic information being transferred between populations.
Gene Flow
Conditions that must be met for allele frequesies in a population to remain constant:
Hardy-Weinberg Principle/Law
-There are no mutations.
-The population size is large and not affected by genetic drift.
-The population is isolated from other populations (no immigration, emigration, or other types of gene flow).
-Mating occurs randomly.
-Natural selection isn’t occurring.
The formation of a new and distinct species (in the course of evolution).
Speciation
The inability of a species to reproduce with related species.
Reproductive Isolation
Reproductive Isolation
Occurring before fertilization. —> Prevents the zygote from being formed.
Prezygotic Isolation
Prezygotic Isolation
Geography separates species or the species find mates in different habitats.
(ex. rivers or mountain rangers, some individuals might establish themselves in a new area)
Habitat Isolation
Prezygotic Isolation
The species mate during different seasons or times of the day.
Temporal Isolation
Prezygotic Isolation
Organisms aren’t attracted to each other. —> Many animals have specific mating rituals that they use to attract mates.
Behavioral Isolation
Prezygotic Isolation
The species are physiologically different enough to NOT be able to mate.
Mechanical Isolation
Prezygotic Isolation
Gametes from the 2 species are unable to fuse to form a zygote.
Gamete Isolation/Genetic Isolation
Reproductive Isolation
Occurring after fertilization. —> Affects the zygote after it’s formed.
Postzygotic Isolation
Postzygotic Isolation
An egg is fertilized but the zygote can’t mature to form offspring.
Zygote Mortality
Postzygotic Isolation
Offspring can be formed but still have a high mortality rate.
Hybrid Inviability
Postzygotic Isolation
Hybrid offspring are unable to reproduce.
(ex. mules)
Hybrid Sterility
Speciation
If habitat isolation causes 2 populations to become reproductively isolated, natural selection may drive these geographically isolated populations to become different species.
Allopatric Speciation
Speciation
A subpopulation is established on the edge of a main population’s habitat becomes a new species (over many generation). —> One population is MUCH smaller than the other.
Peripatric Speciation
Speciation
Subpopulations of a species have different ranges but overlap with each other at least somewhat. —> Tend to mate with geographic neighbors.
Instead of being separated by a physical barrier, differences int eh same environment separate the species.
Parapatric Speciation
Speciation
Formation of new species without geographic isolation. RARE
Barriers to gene flow sometime develop without a physical or geographic barrier.
Sympatric Speciation
Speciation
The evolution of a single species into diverse species adapted to specific niches.
Diversification of species into many niches. —> Happens most rapidly if a change in the environment creates new niches or makes additional resources available.
Adaptive Radiation
When a large number of living species goes extinct in a relatively short time. —> Often followed by periods of high adaptive radiation and speciation.
Mass Extinction
The idea that some species survive a catastrophic even that leads to mass extinction while others don’t.
Catastrophic Species Selection
