Unit 8 - Natural Selection VOCAB

Hardy-Weinberg equilibrium

A mathematical description of the fact that allele and genotype frequencies remain constant in a random-mating population in the absence of inbreeding, seletion, or other evolutionary forces; usually stated: If the frequency of the allele a is p and the frequency of the allele b is q, then the genotype frequencies after one generation of random mating will always be p²+2pq+q² = 1

genotype frequencies

A measure of the occurrence of a genotype in a population, expressed as a proportion of the entire population, for example, an occurrence of 0.25 (25%) for a homozygous recessive genotype

disassortative mating

A type of nonrandom mating in which phenotypically different individuals mate more frequently

genetic drift

Random fluctuation in allele frequencies over time by chance

founder effect

The effect by which rare allele and combinations of allele may be enhanced in new populations

bottleneck

A loss of genetic variability that occurs when a population is reduced drastically in size

selection

The process by which some organisms leave more offspring than competing ones, and their genetic traits tend to appear in greater proportions among members of succeeding generations than the traits of those individuals that leave fewer offspring

fitness

The genetic contribution of an individual to succeeding generations. Relative fitness refers to the fitness of an individual relative to other individuals in a population

Parental investment

The energy and time each sex invests in producing and rearing offspring

intrasexual selection

Competitive interactions among members of one sex to achieve fertilization success

intersexual selection

Selection by members of one sex of which individuals in the other sex will get to mate

secondary sexual characteristics

any physical characteristic developing at puberty which distinguishes between the sexes but is not directly involved in reproduction

sexual dimorphism

Morphological differences between the sexes of a species

sperm competition

Competition among sperm to successfully fertilize a female’s egg

handicap hypothesis

The hypothesis that males will evolve exaggerated traits that are disadvantageous and that by choosing a male with the largest handicap, the females ensure that their offspring will receive these quality genes

Sensory exploitation

Evolution in males of a signal that exploits preexisting sensory biases in females

frequency-dependent selection

A type of selection that depends on how frequently or infrequently a phenotype occurs in a population

oscillating selection

The situation in which selection alternately favors one phenotype at one time, and a different phenotype at another time, for example, during drought conditions versus during wet conditions

heterozygous advantage

The situation in which individuals heterozygous for a trait have a selective advantage over those that are homozygous; an example is sickle cell anemia

disruptive selection

A form of selection in which selection acts to eliminate rather than favor the intermediate type

directional selection

A form of selection in which selection acts to eliminate one extreme from an array of phenotypes

stabilizing selection

A form of selection in which selection acts to eliminate both extremes from a range of phenotypes

industrial melanism

Phrase used to describe the evolutionary process of in which initially light-colored organisms become dark as a result of nature selection

artificial selection

Change in the genetic structure of populations due to selective breeding by humans. Many domestic animal breeds and crop varieties have been produced through artificial selection

homologous structures

Refers to similar structures that have the same evolutionary origin

Pseudogene

A copy of a gene that is not transcribed

Biogeography

The study of the geographic distribution of species

convergent evolution

The independent development of similar structures in organisms that are not directly related; often found in organisms living in similar enviornments

sympatric speciation

The differentiation of populations within a common geographic area into species

gene pool

All the alleles present in a species

biological species concept

The concept that defines species as groups of populations that have the potential to interbreed and that are reproductively isolated from other groups

reproductively isolated

Describing populations whose members do not mate with each other or who cannot produce fertile offspring

reproductive isolating mechanisms

Any barrier that prevents genetic exchange between species

prezygotic isolating mechanisms

A type of reproductive isolation in which the formation of a zygote is prevented; these mechanisms may range from physical separation in different habitats to gametic, in which gametes are incapable of fusing

postzygotic isolating mechanisms

A type of reproductive isolation in which zygotes are produced but are unable to develop into reproducing adults; these mechanisms may range from inviability of zygotes or embryos to adults that are sterile

pheromones

Chemical substance released by one organism that influences the behavior or physiological processes of another organism of the same species. Pheromones serve as sex attractants, as trail markers, and as alarm signals

polyploidy

Condition in which one or more entire sets of chromosomes are added to the diploid genome

autopolyploidy

A polyploid organism that contains a duplicated genome of the same species; may result from a meiotic error

allopolyploidy

A polyploid organism that contains the genomes of two or more different species

adaptive radiations

The evolution of several divergent forms from a primitive and unspecialized ancestor

key innovation

A newly evolved trait in a species that allows members to use resources or other aspects of the environment that were previously inaccessable

character displacement

A process in which natural selection favors individuals in a species that use resources not used by other species. This results in evolutionary change leading to species dissimilar in resource use

gradualism

The view that species change very slowly in ways that may be imperceptible from generation to the next but that accumulate and lead to major changes over thousands or millions of years

punctuated equilibrium

A hypothesis about the mechanism of evolutionary change proposing that long periods of little or no change are punctuated by periods of rapid evolution

mass extinctions

A relatively sudden, sharp decline in the number of species; for example, the extinction at the end of the Cretaceous period in which the dinosaurs and a variety of other organisms disappeared

systematics

The reconstruction and study of evolutionary relationships

phylogeny

The evolutionary history of an organism, including which species are closely related and in what order related species evolved; often represented in the form of an evolutionary tree

ancestral similarity

Similarity among species that is inherited from the most recent common ancestor of an entire group

derived similarity

Similarity that arose more recently—that is, is not inherited form the ancestor of the entire group—and is shared by only a subset of the species

cladistics

A taxonomic technique used for creating hierarchies of organisms that represent true phylogenetic relationship and descent

shared derived characters

In cladistics, character states that are shared by species and that are different from the ancestral character state

character states

In cladistics, one of two or more distinguishable forms of a character, such as the presence or absence of teeth in amniote vertebrates

taxon

Species or higher-level group, such as genus or family

outgroup

A species or group fo species that is closely related to, but not a member of, the group under study

cladogram

A figure that depicts the evolutionary relationships among a group of species or other taxa

clade

A taxonomic group composed of an ancestor and all its descendants

synapomorphy

In systematics, a derived character that is shared by clade members

plesiomorphy

In cladistics, another term for an ancestral character state

symplesiomorphies

In cladistics, another term for a shared ancestral character state

Homoplasy

In claudistics, a shared character state that has not been inherited from a common ancestor exhibiting that state; may result from convergent evolution or evolutionary reversal. The wings of birds and of bats, which are convergent structures, are examples

principle of parsimony

Principle stating that scientists should favor the hypothesis that requires the fewest assumptions

molecular clock

In evolutionary theory, the method in which the rate of evolution of a molecule is constant throughout time

monophyletic

In phylogenetic classification, a group that includes the most recent common ancestor of the group and all its descendants. A clade is monophyletic a group

paraphyletic

In polygenetic classification, a group that includes the most recent common ancestor of the group, but not all its descendants

polyphyletic

In polygenetic classification, a group that does not include the most recent common ancestor of all members of the group

phylogenetic species concept

The concept that defines species on the basis of their phylogenetic relationships