Unit 10: Mechanisms of Evolution

natural selection

A process in which individuals that have certain inherited traits tend to survive and reproduce at higher rates than other individuals because of those traits

variation

Differences between members of the same species

heritable traits

a characteristic that can be passed from parents to offspring through genetic inheritance

differential reproductive success

the phenomenon where certain individuals within a population produce more offspring than others due to advantageous traits or behaviors

adaptation

Inherited characteristic of an organism that enhances its survival and reproduction in a specific environment

fitness

an organism’s ability to survive, reproduce, and pass on its genes to the next generation

artificial selection

The selective breeding of domesticated plants and animals to encourage the occurrence of desirable traits

sexual selection

A process in which individuals with certain inherited characteristics are more likely than other individuals of the same sex to obtain mates

sexual dimorphism

Differences between the secondary sex characteristics of males and females of the same species

coevolution

The joint evolution of two interacting species, each in response to selection imposed by the other

directional selection

Natural selection in which individuals at one end of the phenotypic range survive or reproduce more successfully than do other individuals

disruptive selection

Natural selection in which individuals on both extremes of a phenotypic range survive or reproduce more successfully than do individuals with intermediate phenotypes

stabilizing selection

Natural selection in which intermediate phenotypes survive or reproduce more successfully than do extreme phenotypes

allele frequency (p, q)

the proportion of a specific allele in a population's gene pool, indicating how common that allele is within the population

genotypic frequency (p², 2pq, q²)

the proportion of a specific genotype within a population, calculated by dividing the number of individuals with that genotype by the total number of individuals in the population

Hardy-Weinberg equilibrium

The state of a population in which frequencies of alleles and genotypes remain constant from generation to generation, provided that only Mendelian segregation and recombination of alleles are at work

microevolution

Evolutionary change below the species level; change in the allele frequencies in a population over generations

macroevolution

Evolutionary change above the species level. Examples of macroevolutionary change include the origin of a new group of organisms through a series of speciation events and the impact of mass extinctions on the diversity of life and its subsequent recovery

non-random mating

Non-random mating is when individuals in a population choose their mates based on specific traits rather than randomly

gene flow

The transfer of alleles from one population to another, resulting from the movement of fertile individuals or their gametes

genetic drift

A process in which chance events cause unpredictable fluctuations in allele frequencies from one generation to the next. Effects of genetic drift are most pronounced in small populations

gene pool

The aggregate of all copies of every type of allele at all loci in every individual in a population. The term is also used in a more restricted sense as the aggregate of alleles for just one or a few loci in a population

founder effect

Genetic drift that occurs when a few individuals become isolated from a larger population and form a new population whose gene pool composition is not reflective of that of the original population

bottleneck effect

Genetic drift that occurs when the size of a population is reduced, as by a natural disaster or human actions. Typically, the surviving population is no longer genetically representative of the original population

homologous structure

Structures in different species that are similar because of common ancestry

analogous structure

Structures in different species that are similar because of convergent ancestry

vestigial structure

A feature of an organism that is a historical remnant of a structure that served a function in the organism’s ancestors

fossil

A preserved remnant or impression of an organism that lived in the past

biogeography

The scientific study of the past and present geographic distributions of species

divergent evolution

the process of groups from the same ancestor evolving and forming new species

convergent evolution

The evolution of similar features in independent evolutionary lineages

heterozygote advantage

Greater reproductive success of heterozygous individuals compared with homozygotes; tends to preserve variation in a gene pool