ch 4 Flashcards
(21 cards)
founder effect
potentially biased sampling of the genetic variation in a species due to the isolation of a small number of its members
variability
the tendency of individuals in a population to differ in the expression of a genetic or phenotypic trait;
Variation in populations is also modified by several processes beyond natural selection, including gene flow, genetic drift, and founder effect
Hardy-Weinberg Equilibrium:
conditions under which the frequency of alleles or phenotypes in a natural population remain in equilibrium unless acted on by one or more evolutionary forces
- Mutation does not occur
- The population in effect is indefinitely large
- All members of the population have the potential to mate and all mating is random
- Natural selection is not occurring\
- Migration does not occur
speciation
the way species are defined
can be defined in a number of ways, most commonly in terms of reproductive isolation as the distinguishing feature of the biological species concept.
hybrid zones
ecological regions in which closely related species overlap in occurrence, allowing for interbreeding to occur, producing hybrid offspring
morphospecies
designation of species in the fossil record according to similarity in form irrespective of time
chronospecies
designation of species identity by virtue of the passage of time; two fossils may be deemed species if separated by sufficient time
anagenesis
a pattern of slow, linear evolutionary change, known as Darwinian gradualism
cladogenesis
a pattern of evolution characterized by branching, in which a single species may give rise to one or more “daughter” species that subsequently diverge; known as horizontal speciation
clades
groups of species sharing a closer ancestry among themselves than any of them do with species of other clades
gene flow
the movement of genes with or without the movement of individuals over geographic space
genetic drift
random changes in allele frequencies in small populations independent of selection
genetic bottleneck
a sudden constriction of the genetic diversity appearing in a generation commonly associated with a reduction in population size
homologous traits
referring to homology, which is similar among characters as a result of inheritance from a common ancestor
Similarities among species can occur through shared common ancestry
homoplasies
analogous characters in different taxa that appear as a result of independent evolution; such a character is not present in the last common ancestor of the taxa in question
Similarities among species can occur through through convergent or parallel evolution in the absence of a recent common ancestor
convergence
a path toward development of homoplasy; evolution acts on different ancestral structures to converge upon a similar outcome in response to similar adaptive pressures
parallelism
a path toward development of homoplasy; evolution modifies an ancestral character to achieve similar outcomes in response to similar adaptive pressures
neo-darwinism
- the marriage of mutation as the source of variation with natural selection as the mechanism that determines whether a mutation is helpful (i.e., adaptive) or otherwise.
Sir Julian Huxley “Evolution: The Modern Synthesis” three guiding principles:
(1) selection is the paramount force in evolution
(2) evolution entails gradual change over many generations
(3) evolution occurs within population
classification
can follow either a shared evolution history model (cladistic) or one based on morphological and anatomical similarity (gradistic).
cladistics
Classification of biological diversity that follows a shared evolution history mode
gradistic
classification of biological diversity that is based on morphological and anatomical similarity
