Chapter 4: From Variant to Species Flashcards
founder effect
the potentially biased sampling of the genetic variation in a species due to the isolation of a small number of its members
variants
individuals within populations having different expressions of a trait
variability
the tendency for members of a population to exhibit different versions of a particular trait
variation
the expression of differences for a characteristic among members of a population
population genetics
a science concerned with variation in gene frequencies within the populations and the forces that modify them over time
Hardy-Weinberg (H-W) Equilibrium
a model specifying the 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
heterosis
also known as heterozygote advantage; the tendency for offspring of genetically distinct individuals to have increased vigour as they are less likely to express deleterious recessive alleles, which increase in frequency when males and females with similar genetic background mate
epigenetic
mechanisms acting during mitosis (development) to modify gene expression without modifying the actual DNA sequence; may result in heritable variation
speciation
the formation of new species from pre-existing forms
evo-devo
evolutionary developmental biology; a branch of evolutionary theory that invokes a prominent role for embryonic development and epigenetic mechanisms in the ontogeny and phylogeny of phenotypes
phenotypic plasticity
a potential for individuals to modify their phenotype in response to variation in external conditions in order to maintain homeostasis and function
transgenerational epigenetic inheritance
the transmission of novel phenotypic features from parent to offspring acquired without recourse to modification in DNA base sequences
demes
local breeding populations; a deme is a subset of a species within which most members find a mate
biogeography
the study of the geographic distribution of organisms, habitats, and evolutionary history as it relates to landscape and ecology
sympatric
refers to species that coexist in the same geographic region
allopatric
refers to species that “live apart” and do not occupy the same geographic locale; allopatric species are presumed to exist in genetic isolation
parapatric
refers to species whose ranges are contiguous but not overlapping; gene flow is possible
hybrid zones
ecological regions in which closely related species overlap in occurrence, allowing for interbreeding to occur, producing hybrid offspring
recognition species concept (RSC)
a concept of the species as a group whose members, according to particular cues, identify potential mates with whom they might successfully interbreed (in contract, the BSC emphasizes an absence of breeding potential)
conspecific
belonging to the same species
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
tempo and mode of evolution
refers to the pace and manner of evolutionary change
anagenesis
a pattern of slow, linear evolutionary change, also known as Darwinian gradualism
phyletic evolution
an alternative term for anagenesis, with “phyletic” denoting a line of direct ancestor-descendant relationship
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; also known as horizontal speciation
clades
groups of species sharing a closer ancestry among themselves than any of them do with species of other clades
punctuated equilibrium
a pattern of evolution characterized by periods of stasis interrupted by rapid evolutionary change; more commonly found in small, peripheral populations on the edge of a species range
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
directional selection
a form of positive or negative selection resulting in a shift in phenotypes toward one end of the distribution, typically occurring in dynamic and changing environments
lactase persistence
in humans, the continued production past childhood of the enzyme lactase necessary for digesting the milk sugar lactose
stabilizing selection
a form of selection favouring the most common phenotype at the expense of extreme expressions of a character
diversifying selection
a form of positive selection favouring the extremes of the distribution of phenotypes and/or negative selection against the most common expression; may result in sympatric speciation
adaptive radiation
the opportunistic and relatively rapid diversification of new forms into new ecological zones through a series of speciation events
model organism
an extensively studied and well-understood species from which new insights into human biology and disease might be obtained; examples range from bacteria such as E. coli to mammals such as mice
constraint
genetic or functional limitation on the activity or expression of a characteristic
adaptationist
a perspective that commonly seeks an adaptive explanation or mechanism for the presence or form of a particular phenotypic character
biological reductionism
a method of analysis that argues that biological complexity can be explained in terms of physical laws applied to individual parts
inbreeding depression
reduced vigour in an organism by virtue of increased homozygosity resulting from mating between related individuals having similar DNA
balanced polymorphism
polymorphism means “many types” and in genetic terms denotes phenotypes established at proportions that do not require mutation to maintain their existence. Balanced polymorphism occurs when a heterozygote has a selective advantage over alternative homozygotes, thereby maintaining allele diversity within the population
polydactyly
a congenital condition in which an individuals has more than five fingers or toes on hands or feet; one side or both many be affected
Tay-Sachs
a genetic disease affecting neurological development caused by a mutation on chromosome 15; the most common form occurs in infancy and early childhood and is fatal within the first five years of life
genetic screening
a practice in medical genetics involving identification of potentially harmful genotypes
genetic bottleneck
a sudden constriction on the genetic diversity appearing in a generation, commonly associated with a reduction in population size
cladistic
a taxonomic method emphasizing phylogenetic relatedness and based on the existence of clades composed of members of evolving lineages
gradistic
a taxonomic method that groups forms into named categories (the major units of which are termed “grades”) based on similarity of form, behaviour, and/or ecology; also known as phenetics
cladogram
a branching depiction of relationships among taxa based on proximity of evolutionary descent
homologous traits
referring to homology, which is similarity among characters as a result of inheritance from a common ancestor
homoplasies
analogous characters in different taxa that appear as a result of independent evolution; such a character (the singular form is “homoplasy”) is not present in the last common ancestor of the taxa in question
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
