Evolution, Phylogeny, and Population Genetics

Comprehensive fill-in-the-blank practice flashcards covering phylogeny reconstruction, the biological species concept, speciation mechanisms, Darwinian evolution, and population genetics across Exam 2 lecture materials.

Systematics

The scientific discipline concerned with classifying organisms and determining their evolutionary relationships through time using fossil, molecular, and genetic data.

Taxonomy

The scientific field dedicated to the identification, description, naming, and classification of organisms.

Binomial Nomenclature

The two-part scientific naming system for species instituted by Carolus Linnaeus, consisting of the genus name (capitalized) followed by the specific epithet (lowercase), both italicized.

Taxon

A named taxonomic unit at any given level of the biological classification hierarchy.

PhyloCode

A proposed protocol in systematic biology that designates only monophyletic groups—those containing a common ancestor and all its descendants—as taxonomically valid.

Sister Taxa

Groups of organisms that share an immediate common ancestor that is not shared by any other group.

Basal Taxon

A lineage that diverges early in the evolutionary history of a group and originates near the common ancestor of the group.

Polytomy

A branch point on a phylogenetic tree from which more than two descendant taxa emerge, signifying an unresolved divergence relationship.

Cladistics

An analytical approach to systematics that reconstructs phylogenetic relationships by categorizing organisms into clades based on shared characters.

Monophyletic Group

A clade consisting of an ancestral species and all of its descendants, representing a real natural grouping.

Paraphyletic Group

An unnatural evolutionary grouping that includes an ancestral species and some, but not all, of its descendants.

Polyphyletic Group

An unnatural evolutionary grouping consisting of taxa derived from two or more distinct ancestral sources.

Synapomorphy

A shared derived character that is an evolutionary novelty unique to a particular clade and used to diagnose monophyletic groups.

Symplesiomorphy

A shared ancestral character that originated in an ancestor that predates the common ancestor of the specific clade under study.

Autapomorphy

A uniquely derived character that appears on only a single lineage branch on a phylogenetic tree and is not shared with any other taxon.

Maximum Parsimony

The principle stating that when considering multiple phylogenetic hypotheses, the tree requiring the fewest evolutionary steps or character-state changes is preferred.

Maximum Likelihood

An approach applied to molecular trees that selects the tree topology that reflects the most likely sequence of evolutionary events under the assumption of a constant rate of DNA change.

Orthologous Genes

Homologous genes found in a single copy within a genome that diverge only after a speciation event occurs.

Paralogous Genes

Homologous genes that arise through gene duplication within a genome, providing extra gene copies that can diverge and acquire novel functions.

Neutral Theory

The hypothesis proposing that the majority of evolutionary mutations in genes and proteins have no significant effect on fitness, accumulating at a roughly constant rate independent of natural selection.

Horizontal Gene Transfer

The movement of genetic material between genomes of unrelated organisms via transposable elements, viral infections, plasmids, or organismal fusion.

Speciation

The evolutionary process by which a single ancestral lineage splits into two or more distinct, reproductively isolated biological species.

Macroevolution

Broad patterns of evolutionary change occurring above the species level, including the emergence of novel features and whole taxonomic groups.

Biological Species Concept

The species definition stating that a species is a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring, and do not successfully interbreed with other groups.

Reproductive Isolation

The presence of biological barriers that prevent members of two different species from mating and producing viable, fertile offspring.

Habitat Isolation

A prezygotic barrier where two species encounter each other rarely or not at all because they occupy different ecological habitats within the same geographic area.

Temporal Isolation

A prezygotic reproductive barrier occurring when species breed at different times of the day, during different seasons, or in different years.

Behavioral Isolation

A prezygotic reproductive barrier involving specific courtship rituals, mating calls, or display behaviors that are unique to a particular species.

Mechanical Isolation

A prezygotic reproductive barrier where morphological differences prevent the successful completion of mating or copulation.

Gametic Isolation

A prezygotic reproductive barrier where biochemical incompatibility prevents the sperm of one species from fertilizing the egg of another species.

Reduced Hybrid Viability

A postzygotic reproductive barrier where genetic incompatibilities between parental species impair hybrid development or result in frail, non-viable offspring.

Reduced Hybrid Fertility

A postzygotic reproductive barrier where hybrid individuals develop into vigorous adults but are sterile and cannot produce functional gametes.

Hybrid Breakdown

A postzygotic barrier where first-generation ($F_1$) hybrids are viable and fertile, but subsequent generations ($F_2$) produced by backcrossing or inbreeding are weak or sterile.

Morphological Species Concept

An approach that defines a species based on distinctive anatomical and structural traits, applicable to both sexual and asexual organisms as well as fossils.

Ecological Species Concept

A species definition that distinguishes species based on their ecological niche and role in the biological community, emphasizing disruptive selection.

Phylogenetic Species Concept

The definition of a species as the smallest cluster of organisms on a phylogenetic tree that shares a unique common ancestor.

Allopatric Speciation

Speciation that takes place when a parent population is subdivided into geographically isolated subpopulations that diverge independently.

Sympatric Speciation

Speciation that occurs in populations that occupy overlapping geographic distributions, typically driven by habitat differentiation, sexual selection, or polyploidy.

Ring Species

A continuous geographic loop of interbreeding populations whose terminal populations overlap geographically but are reproductively isolated from one another.

Hybrid Zone

A geographic contact region where individuals of closely related species meet, mate, and produce offspring of mixed ancestry.

Reinforcement

An outcome in a hybrid zone where natural selection strengthens prezygotic barriers to prevent mating that produces unfit hybrids, decreasing hybridization over time.

Punctuated Equilibrium

A model of evolutionary tempo characterized by long periods of evolutionary stasis punctuated by brief, rapid intervals of speciation.

Scala Naturae

Aristotle's philosophical hierarchy arranging all life forms along an unchanging scale or ladder of increasing complexity.

Catastrophism

Georges Cuvier's hypothesis that boundaries between geological strata represent localized catastrophic events that wiped out species, rather than gradual evolutionary changes.

Uniformitarianism

Charles Lyell's principle stating that the physical and geological processes shaping Earth today operated at the same continuous rates throughout deep geologic time.

Inheritance of Acquired Characteristics

Lamarck's incorrect evolutionary mechanism stating that morphological modifications acquired during an individual's lifetime can be transmitted to its offspring.

Adaptation

An inherited characteristic that enhances an organism's ability to survive and successfully reproduce within a specific environment.

Natural Selection

The evolutionary mechanism whereby individuals possessing advantageous heritable traits survive and reproduce at higher rates than other individuals in a given environment.

Artificial Selection

The selective breeding of domesticated species by humans through choosing individuals with desired phenotypes to breed over successive generations.

Homologous Structures

Anatomical structures present in different species that share underlying skeletal or developmental similarities inherited from a common ancestor, regardless of divergence in function.

Homoplasy

A shared phenotypic or molecular trait that evolved independently in distinct lineages rather than being inherited from a common ancestor.

Convergent Evolution

The independent evolutionary development of similar adaptive features in distantly related lineages facing comparable environmental demands.

Vestigial Structures

Remnant anatomical features in an organism that served crucial functions in ancestral lineages but have little to no utility in modern descendants.

Microevolution

Evolutionary change on its smallest scale, characterized by shifts in allele frequencies within a population across successive generations.

Average Heterozygosity

A quantitative measurement of gene variability in a population calculated as the average percentage of genetic loci that are heterozygous.

Cline

A graded, continuous geographic variation in an inherited trait or allele frequency across an environmental or geographic gradient.

Gene Pool

The total collection of all alleles for all gene loci present across every individual within an interbreeding population.

Hardy-Weinberg Principle

The model stating that allele and genotype frequencies in a population remain constant from generation to generation in the absence of evolutionary forces ($p^2 + 2pq + q^2 = 1$ and $p + q = 1$).

Genetic Drift

Unpredictable fluctuations in allele frequencies from one generation to the next caused entirely by chance events, operating most strongly in small populations.

Founder Effect

A form of genetic drift occurring when a small number of colonizing individuals establishes a new population with an allele pool distinct from the parent population.

Bottleneck Effect

A sudden, drastic reduction in population size and genetic diversity resulting from an environmental catastrophe or severe population collapse.

Gene Flow

The transfer of genetic alleles between different populations via the migration and reproduction of fertile individuals or the transport of gametes.

Relative Fitness

The contribution an individual makes to the gene pool of the subsequent generation relative to the contributions of other individuals in the population.

Directional Selection

A mode of natural selection that favors individuals displaying phenotypes at one extreme end of the phenotypic range.

Disruptive Selection

A mode of natural selection that favors individuals at both ends of the phenotypic spectrum while selecting against intermediate variants.

Stabilizing Selection

A mode of natural selection that favors intermediate phenotypic variants by acting against individuals with extreme phenotypes.

Sexual Dimorphism

Distinct physical, structural, or coloration differences between males and females of the same species resulting from sexual selection.

Intrasexual Selection

A form of sexual selection involving direct competition between members of one sex (commonly males) to win mating opportunities with the opposite sex.

Intersexual Selection

A form of sexual selection (mate choice) wherein individuals of one sex (frequently females) exhibit specific preferences when choosing their mating partners.

Heterozygote Advantage

A form of balancing selection occurring when heterozygous individuals at a particular locus exhibit higher reproductive fitness than both homozygous genotypes.

Frequency-Dependent Selection

A type of balancing selection where the evolutionary fitness of a phenotype decreases as it becomes more prevalent within a population.

The discipline concerned with the diversity and evolutionary relationships of organisms through time is called __________.

systematics

The identification, description, naming, and classification of organisms is known as __________.

taxonomy

A depiction of the evolutionary history of groups of related species showing their relationships is a(n) __________.

cladogram

In the 18th century, Carolus Linnaeus published a system of taxonomy based on resemblances and introduced a two-part naming format known as __________.

binomial nomenclature

In binomial nomenclature, the first part of a species name is the genus, and the second part is called the __________.

specific epithet

A named taxonomic unit at any level of the Linnaean hierarchy is called a(n) __________.

taxon

A proposed protocol that recognizes only groups that include a common ancestor and all its descendants as taxonomically valid is called __________.

PhyloCode

In a phylogenetic tree, groups of organisms that share an immediate common ancestor not shared by any other group are called __________.

sister taxa

A lineage in a phylogenetic tree that diverges early in the history of a group and originates near the common ancestor is a(n) __________.

basal taxon

A branch point in a phylogenetic tree from which more than two descendant groups emerge, typically signifying unresolved evolutionary relationships, is a(n) __________.

polytomy

A valid clade is __________, signifying that it consists of an ancestral species and all of its descendants.

monophyletic

In this diagram, the highlighted box illustrates a(n) __________ grouping because it consists of an ancestral species and some, but not all, of its descendants.

paraphyletic

A grouping that consists of various species derived from different ancestral lineages and lacks a common ancestor unique to the group is __________.

polyphyletic

A shared derived character that is an evolutionary novelty unique to a particular clade is known as a(n) __________.

synapomorphy

A shared ancestral character that originated in an ancestor prior to the common ancestor of the clade being analyzed is called a(n) __________.

symplesiomorphy

A self-derived character that appears only on a single terminal branch and is not shared with any other taxon in the tree is a(n) __________.

autapomorphy

In phylogenetic analysis, character polarity is determined using a(n) __________, a species or group closely related to but outside the ingroup.

outgroup

The principle of __________ assumes that the phylogenetic tree requiring the fewest evolutionary events or character transitions is the most likely.

maximum parsimony

Assuming a constant rate of DNA evolution over time, the tree reflecting the most likely sequence of evolutionary events is found using the principle of __________.

maximum likelihood

According to the divergence scale on this phylogenetic tree, the total number of nucleotide changes along the branches separating Sample B and Sample C is __________.

$$18$$

DNA coding for rRNA evolves slowly and is useful for deep time branching, whereas __________ evolves rapidly and is used to explore recent evolutionary divergences.

mtDNA

Genes that result from gene duplication, are present in multiple copies within a genome, and can diverge to take on new functions are called __________ genes.

paralogous

The __________ states that much evolutionary change in genes and proteins has no effect on fitness and is not influenced by natural selection.

neutral theory

The movement of genes between genomes of unrelated organisms via transposable elements, plasmids, viral infection, or fusion is called __________.

horizontal gene transfer

The evolutionary process by which one species splits into two or more new species is called __________.

speciation

Broad patterns of evolutionary change above the species level, such as the origin of entire taxonomic groups, are referred to as __________.

macroevolution

The biological species concept defines a species as a group of populations whose members have the potential to interbreed and produce __________ offspring.

viable, fertile

Reproductive barriers that impede mating or hinder fertilization if mating occurs are classified as __________ barriers.

prezygotic

When two species rarely or never encounter each other because they occupy different habitats, they are separated by __________ isolation.

habitat