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a system of classification which groups taxa together according to the characteristics which have most recently evolved

Primitive Traits

are characteristics which have the same structure and function and which evolved early on in the organisms being studied

Derived Traits

characteristics which have the same structure and function but which evolved more recently as modifications of a previous trait


a monophyletic group composed of the most recent common ancestor of the group and all its descendants

usually made up of several species


characteristics are derived from the same part of a common ancestor


characteristics which may have the same function but they do not necessarily have the same structure and they are not derived from a common ancestor

Genetic Drift

the unpredictable fluctuations in allele frequencies in a gene pool of a population from one generation to the next

Gene Flow

involves fertile individuals moving from one population to to another which means they are removing specific genes from one population and introducing the genes into another population


a condition where the organism has more than two complete sets of chromosomes


occurs when an individual has more than two sets of chromosomes from a single species


occurs when two different species interbreed and produce a hybrid that is often sterile


the process by which new species arise from an existing population

Allopatric Speciation

occurs when a geographical barrier creates a barrier to gene flow

Sympatric Speciation

occurs when the populations occupy the same geographical area or range

Parapatric Speciation

a type of divergence in a population where an ancestral stock splits into groups which share some geographical territory but specialization for particular niches and reduced fitness of the heterozygotes leads to breeding separation

Adaptive Radiation

the evolution of several species from a common ancestor due to natural selection

Convergent Evolution

leads to superficial similarities due to organisms living in the same habitat or having the same lifestyle even though they are not closely related (population will look similar)

Divergent Evolution

occurs when different groups arise from a common ancestor due to adaptive radiation

Allele Frequency


Genotype Frequency


Frequency Of Homozygous Dominant

p^2 (TT) (phenotype)

Frequency Of Heterozygote

2pq (Tt) (phenotype)

Frequency Of Dominant Allele


Frequency Of Homozygous Recessive


Frequency Of Recessive Allele


Similarities Between Divergent And Convergent Evolution

both occur to natural selection

Parallel Evolution

occurs when different species maintain a certain degree of similarity while both populations are changing and evolving along independent paths

Gradualism And Punctuated Equilibrium

gradualism is a slight change in the population of each generation so that over time these changes lead to the evolution of a new species. punctuated equilibrium is when species remain changed for long lengths of time in a period of stasis, to be replaced very quickly by a new species (grasshoppers)

Directional Selection

shifts the population in one direction favoring a phenotype at one end of the variation

Disruptive Selection

Shifts the population to both extremes of the phenotypic range

Stabilizing Selection

shifts the population to the intermediate form with the extreme variants less favored

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