SPECIATION & ISOLATION
This type of isolation occurs when a physical barrier like a river or mountain range prevents populations from interbreeding.
geographic isolation
This process occurs when organisms move across a barrier to colonize a new area
dispersal
his mechanism introduces entirely new alleles into a population
Mutation
Evolution is defined as a change in this within a population over time.
allele frequency
This mode of selection favors individuals with intermediate phenotypes.
stabilizing selection
When two populations live in the same area but breed at different times of year, this reproductive barrier is at work.
temporal isolation?
The formation of a river that splits a once-continuous population is an example of this process
vicariance
Random changes in allele frequencies that have the strongest effects in small populations
genetic Drift
A population with no mutation, migration, selection, or drift would meet the conditions of this principle
Hardy–Weinberg equilibrium
This mode of selection favors one extreme phenotype, often following environmental change.
Directional Selection
A chromosomal mutation that instantly creates reproductive isolation and is common in plant speciation
polyploidy
Island populations that are genetically nested within mainland lineages most strongly support this process.
dispersal
This mechanism can prevent speciation by homogenizing allele frequencies between populations.
Gene flow
this evolutionary force can counteract local adaptation by introducing maladaptive alleles.
Gene flow
This mode of selection favors both extremes while selecting against intermediate phenotypes.
disruptive selection
A population split by a geographic barrier accumulates genetic differences over time through mutation and drift, eventually forming two species even if the barrier disappears.
allopatric speciation
Continental drift separating South America and Africa and leading to species divergence best illustrates this mechanism.
vicariance
A severe population reduction that causes loss of genetic diversity and alters allele frequencies by chance.
Bottleneck effect
When selection favors different traits in different environments, leading to divergence between populations.
divergent selection
This mode of natural selection maintains multiple alleles in a population when heterozygotes have higher fitness than either homozygote.
balancing selection
This form of isolation results when populations diverge genetically to the point that hybrids are inviable or sterile, even if mating occurs
What is postzygotic reproductive isolation
The Amazon River separating species pairs on opposite banks, with divergence timing matching river formation, supports this evolutionary explanation.
vicariance
the only evolutionary mechanism that consistently produces adaptations by increasing fitness-related alleles.
Natural Selection
Speciation is most likely when gene flow is low and these two mechanisms act independently in isolated populations.
mutation and genetic drift
Seen in systems such as sickle-cell alleles in malarial regions, this mode of selection preserves genetic variation through mechanisms like heterozygote advantage or negative frequency-dependent selection.
balancing selection