AP Biology Unit 7

Genetic drift

Small populations can have chance events that largely alter the allele frequencies

The Founder Effect

A few individuals from a population start a new population with a different allele frequency than the original population

The Bottleneck Effect

Sudden changes in the environment can drastically reduce the size of a population and by chance alone, certain alleles are over or under represented among the surviving individual

Diploidy

Preserves the recessive allele because it can’t be selected against unless an individual has two copies

Frequency dependent selection

The fitness of a phenotype declines if it becomes too common

Temporal isolation

Different species mate at different times of the year

Mechanical isolation

Organisms have incompatible parts for reproduction

Gametic isolation

Organisms have gamete receptors that prevent fertilization from other species

Allopatric speciation

New species arise because a population is geographically isolated from its parent population

Sympatric speciation

No geographical separation but a new species arises from a parent population

Polyploidy

More than two sets of chromosomes in an organism leads to immediate speciation

Evolution

The process by which modern organisms have descended from ancient organisms due to gradual changes over time

Fitness

Ability of an individual to survive and reproduce

Adaptations

Characteristics that increase a chance of survival in their specific environment

Fossil record

Shows the evolutionary changes that occurred over time in various groups of organisms (can be dated by location, depth, and rate of isotope decay)

Anatomical homologies

Structures represent variations that were present in their common ancestor

Vestigial structures

Remnants of features that served important functions in the organism’s ancestor

Molecular homologies

All forms of life use the same genetic code and share genes

Directional selection

Shifts the overall makeup of the population by favoring variants at one extreme of the distribution

Disruptive selection

Favors variants at both ends of the distribution

Stabilizing selection

Removes extreme variants from the population and preserves intermediate types

Sexual dimorphism

Differences in secondary sexual characteristics not associated with reproduction (size, color, ornamentation, behavior)

Neutral variation

DNA variation that has little or no impact on reproductive success

Microevolution

Changes in allele frequencies in a population over time

Macroevolution

The broad pattern of evolution over long time spans

Biological species concept

A species is defined as a population of organisms who have the potential to interbreed in nature and produce living, fertile offspring but are unable to reproduce with other populations of organisms

Habitat isolation

Species are unable to mate due to geographical or habitat differences

Behavioral isolation

Species have specific mating rituals that are not recognized by other species (no mating)

Reduced hybrid viability

Parental genes impair the offspring’s development or survival

Reduced hybrid fertility

Offspring is not fertile and cannot reproduce

Hybrid breakdown

First generation is fine but the following generations have complications

Gradualism

The proposal that species descended from a common ancestor and gradually diverged more and more in structure and function as they acquired unique adaptations

Punctuated equilibrium

The term used to describe long period where species remain unchanged and then are suddenly changed (rapid speciation)

Adaptive radiation

The rapid evolution of species when new habitats open

Phylogeny

The evolutionary history of a species or group of related species

Taxonomy

The ordered division and naming of organisms

Binomial nomenclature

The two-part scientific name of a species (the first part is the genus and the second part is unique for each species within the genus)

Hierarchical classification

Linnaeus introduced a system for grouping species in increasingly inclusive categories (domain, kingdom, phylum, class, order, family, genus, species)

Taxon

A taxonomic unit at any level of hierarchy

Branch point

Represents the divergence of two species

Sister taxa

Groups that share an immediate common ancestor

Homplasies

Analogous structures or molecular sequences that evolved independently

Cladistics

The grouping of organisms by common descent

Clade (monophyletic)

A group of species that includes an ancestral species and all of its descendents

Paraphyletic

An ancestral species and some, but not all, of the descendents

Polyphyletic

Various species that lack a common ancestor

Ingroup

The lineage of organisms that we are studying

Shared ancestral character

A character that originated in an ancestor of the taxon (applies to all the organisms in the phylogenetic tree)

Shared derived character

An evolutionary novelty unique to a particular clade

Outgroup

A closely related species that diverged before the lineage being studied

Maximum parsimony

The hypothesis with the simplest explanation is the best

Molecular clock

Constant rate of evolution in some genes is used to estimate the absolute time of evolutionary change

Protocells

Membrane-bound droplets that maintained different internal chemistry than surroundings

Ribozymes

Self-replicating molecules that made inheritance possible