Chapter 4: From Variant to Species

Question 1

founder effect

Answer 1

the potentially biased sampling of the genetic variation in a species due to the isolation of a small number of its members

Question 2

variants

Answer 2

individuals within populations having different expressions of a trait

Question 3

variability

Answer 3

the tendency for members of a population to exhibit different versions of a particular trait

Question 4

variation

Answer 4

the expression of differences for a characteristic among members of a population

Question 5

population genetics

Answer 5

a science concerned with variation in gene frequencies within the populations and the forces that modify them over time

Question 6

Hardy-Weinberg (H-W) Equilibrium

Answer 6

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

Question 7

heterosis

Answer 7

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

Question 8

epigenetic

Answer 8

mechanisms acting during mitosis (development) to modify gene expression without modifying the actual DNA sequence; may result in heritable variation

Question 9

speciation

Answer 9

the formation of new species from pre-existing forms

Question 10

evo-devo

Answer 10

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

Question 11

phenotypic plasticity

Answer 11

a potential for individuals to modify their phenotype in response to variation in external conditions in order to maintain homeostasis and function

Question 12

transgenerational epigenetic inheritance

Answer 12

the transmission of novel phenotypic features from parent to offspring acquired without recourse to modification in DNA base sequences

Question 13

demes

Answer 13

local breeding populations; a deme is a subset of a species within which most members find a mate

Question 14

biogeography

Answer 14

the study of the geographic distribution of organisms, habitats, and evolutionary history as it relates to landscape and ecology

Question 15

sympatric

Answer 15

refers to species that coexist in the same geographic region

Question 16

allopatric

Answer 16

refers to species that “live apart” and do not occupy the same geographic locale; allopatric species are presumed to exist in genetic isolation

Question 17

parapatric

Answer 17

refers to species whose ranges are contiguous but not overlapping; gene flow is possible

Question 18

hybrid zones

Answer 18

ecological regions in which closely related species overlap in occurrence, allowing for interbreeding to occur, producing hybrid offspring

Question 19

recognition species concept (RSC)

Answer 19

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)

Question 20

conspecific

Answer 20

belonging to the same species

Question 21

morphospecies

Answer 21

designation of species in the fossil record according to similarity in form irrespective of time

Question 22

chronospecies

Answer 22

designation of species identity by virtue of the passage of time; two fossils may be deemed species if separated by sufficient time

Question 23

tempo and mode of evolution

Answer 23

refers to the pace and manner of evolutionary change

Question 24

anagenesis

Answer 24

a pattern of slow, linear evolutionary change, also known as Darwinian gradualism

Question 25

phyletic evolution

Answer 25

an alternative term for anagenesis, with "phyletic" denoting a line of direct ancestor-descendant relationship

Question 26

cladogenesis

Answer 26

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

Question 27

clades

Answer 27

groups of species sharing a closer ancestry among themselves than any of them do with species of other clades

Question 28

punctuated equilibrium

Answer 28

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

Question 29

gene flow

Answer 29

the movement of genes with or without the movement of individuals over geographic space

Question 30

genetic drift

Answer 30

random changes in allele frequencies in small populations, independent of selection

Question 31

directional selection

Answer 31

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

Question 32

lactase persistence

Answer 32

in humans, the continued production past childhood of the enzyme lactase necessary for digesting the milk sugar lactose

Question 33

stabilizing selection

Answer 33

a form of selection favouring the most common phenotype at the expense of extreme expressions of a character

Question 34

diversifying selection

Answer 34

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

Question 35

adaptive radiation

Answer 35

the opportunistic and relatively rapid diversification of new forms into new ecological zones through a series of speciation events

Question 36

model organism

Answer 36

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

Question 37

constraint

Answer 37

genetic or functional limitation on the activity or expression of a characteristic

Question 38

adaptationist

Answer 38

a perspective that commonly seeks an adaptive explanation or mechanism for the presence or form of a particular phenotypic character

Question 39

biological reductionism

Answer 39

a method of analysis that argues that biological complexity can be explained in terms of physical laws applied to individual parts

Question 40

inbreeding depression

Answer 40

reduced vigour in an organism by virtue of increased homozygosity resulting from mating between related individuals having similar DNA

Question 41

balanced polymorphism

Answer 41

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

Question 42

polydactyly

Answer 42

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

Question 43

Tay-Sachs

Answer 43

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

Question 44

genetic screening

Answer 44

a practice in medical genetics involving identification of potentially harmful genotypes

Question 45

genetic bottleneck

Answer 45

a sudden constriction on the genetic diversity appearing in a generation, commonly associated with a reduction in population size

Question 46

cladistic

Answer 46

a taxonomic method emphasizing phylogenetic relatedness and based on the existence of clades composed of members of evolving lineages

Question 47

gradistic

Answer 47

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

Question 48

cladogram

Answer 48

a branching depiction of relationships among taxa based on proximity of evolutionary descent

Question 49

homologous traits

Answer 49

referring to homology, which is similarity among characters as a result of inheritance from a common ancestor

Question 50

homoplasies

Answer 50

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

Question 51

convergence

Answer 51

a path toward development of homoplasy; evolution acts on different ancestral structures to converge upon a similar outcome in response to similar adaptive pressures

Question 52

parallelism

Answer 52

a path toward development of homoplasy; evolution modifies an ancestral character to achieve similar outcomes in response to similar adaptive pressures