Mechanisms Of Evolution Flashcards
What can break the Hardy-Weinberg equilibrium and cause evolution?
Mutations
Non-random mating
Natural selection
Genetic drift
Gene flow
What is significant about mutations?
They are completely random
What are mutations?
Changes in the DNA sequence of an organism (insertion, deletions, substitution at one or more sites)
Mutation contributes to…
Genetic variation
Mutation can…
Modify allele frequencies
Be good, bad or neutral
What is non-random mating?
It occurs when probability that two individuals in a population will mate is not the same for all possible pairs
What does non-random mating affect?
It affects the frequencies of homozygous and heterozygous genotypes
Natural selection is the only mechanism that…
Consistently leads to adaptive change
Natural selection is NOT…
Random
Predictive
Natural selection consistently…
Increases frequency of alleles that provide fitness benefits which leads to adaptive evolution
What are the types of natural selection.
Directional
Stabilizing
Disruptive
Balancing
Sexual selection
When does directional selection occur?
When conditions favor individuals with on extreme of a phenotypic range
How does directional selection shift?
Shifts the frequency curve in one direction (left or right)
Directional selection tends to…
Reduce genetic variation
Stability selection acts against…
Both extreme phenotypes and favors intermediate variants (mean trait value)
Stabilizing selection reduces…
Variation
Stabilizing selection maintains…
Status quo for a particular phenotypic trait
Stabilizing Selection there is no change in…
Average trait value over time
Disruptive selection occurs…
When conditions favor individuals at both extreme of a phenotypic range over individuals with intermediate phenotypes
Disruptive Selection tends to…
Increase genetic variation
Disruptive Selection can lead to…
Speciation (two different species)
How does stabilizing selection look on a graph?
Culls extreme variations
Narrows width of distribution
How does directional selection look on a graph?
Favors one extreme
Shifts distribution left/right
How does disruptive selection look on a graph?
Favors both extremes
Creates bio dual distribution
What is balancing selection?
Selection may preserve variation at some loci, thus maintaining two or more phenotypic forms
What are the two types of balancing selection?
Frequency dependent selection and heterozygote advantage
What is frequency dependent selection?
Fitness of a phenotype depends on how common it is in the population
What is a heterozygote advantage?
When individuals are heterozygous at a particular locus have greater fitness than both kinds of homozygotes , fitness is relative to others in the population and in the environment
What is sexual selection?
Process where individuals with certain inherited characteristics are mo re likely than other individuals of the same sex to obtain mates
What is sexual dimorphism?
Difference in the secondary sexual characteristics between males and females of same species
What is intersexual selection?
Selection within the same sex
What is intersexual selection?
Individuals of one sex are choosy when selecting mates from the other sex; also called mate choice
Why doesn’t natural selection create perfect organisms?
Selection can only act on existing variation
Evolution is not forward looking
Limited by historical constraints
Adaptations often compromises
Interactions with other evolutionary processes and chance events
What is genetic drift?
Chance events that cause allele frequencies to change unpredictability from one generation to the next, especially in small populations
Genetic drift is significant in…
Small populations
Genetic drift causes…
allele frequencies to change at random
Genetic drift leads to…
A loss of genetic variation in a population
Genetic drift can cause…
Harmful alleles to be fixed
What are the two types of genetic drift?
Founder effect and bottleneck effect
What is the founder affect?
When a few individuals become isolated from a larger population and go on to establish a new population whose gene pool differs from the source population
What is the bottleneck effect?
A drastic reduction in the size of a population by chance alone that leads to certain alleles that are over represented/underrepresented among the survivors
What is gene flow? Yeah
Aka migration, transfer of alleles in or out of a populations due to the movement of fertile individuals or their gametes
Gene flow can help or hinder natural selection forces by…
Affecting how well populations are adapted to local environmental conditions
