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