SB0014: Variation, Selection, Speciation, and Evolution

Comprehensive practice flashcards defining key vocabulary across variation, natural and artificial selection, speciation, and evolutionary mechanisms from the SB0014 course lecture.

Variation

The differences that exist between organisms of the same species, arising from gene mutation and environmental factors, which can be inherited.

Biological Species Concept

The concept defining a species as a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring, and do not breed successfully with other populations.

Inherited Variation

Genetically fixed differences among individuals caused by gene activity that are passed down from parents to offspring.

Acquired Variation

Nonheritable characteristics that result from individual activities, nutritional differences, or environmental factors during an organism's lifetime.

Continuous Variation

A type of variation where individuals display a smooth gradation in a measurable quantitative characteristic between two extremes, typically controlled by polygenic inheritance and strongly influenced by the environment.

Discontinuous Variation

A type of variation where individuals fall into a limited number of distinct, qualitative phenotypic categories without intermediate states, typically controlled by one or a few genes and unaffected or minimally affected by the environment.

Natural Selection

The mechanism of evolution defined as differential reproductive success among phenotypes, where biological and environmental agents favor the survival and reproduction of individuals with advantageous heritable traits.

Directional Selection

A mode of natural selection where individuals at one extreme end of the phenotypic range are favored, shifting the population mean toward that extreme over generations.

Stabilizing Selection

A mode of natural selection where intermediate phenotypes are favored while both extreme forms are selected against, maintaining the population mean and reducing overall variation.

Disruptive Selection

A mode of natural selection where individuals at both extremes of the phenotypic range are favored over intermediate forms, often occurring in environments with two distinct ecological niches.

Sexual Selection

A form of selection where one sex (usually females) selects mates among available individuals based on preferred masculine traits, or where individuals compete with members of the same sex for mating access.

Artificial Selection

The intentional or unintentional modification of a species through human action by selecting and breeding individuals that possess desired traits.

Speciation

The evolutionary process through which new species are formed from existing ancestral species, driven by reproductive isolating mechanisms.

Allopatric Speciation

The formation of new species that occurs when a population becomes geographically isolated into two or more subpopulations that evolve independently.

Sympatric Speciation

The emergence of a new species within the parent population without geographic isolation, occurring while populations inhabit the same physical area.

Prezygotic Barriers

Reproductive isolating mechanisms that prevent mating attempts, impede the successful completion of mating, or hinder fertilization between different species.

Habitat Isolation

A prezygotic barrier in which two species encounter each other rarely or not at all because they occupy different habitats within the same general area, without physical separation.

Temporal Isolation

A prezygotic barrier where species that breed at different times of the day, during different seasons, or in different years cannot interbreed.

Behavioral Isolation

A prezygotic barrier where species-specific courtship rituals, mating calls, or other unique behavioral displays prevent different species from recognizing each other as mates.

Mechanical Isolation

A prezygotic barrier where morphological and structural differences in reproductive anatomy prevent successful copulation or pollen transfer.

Gametic Isolation

A prezygotic barrier where molecular incompatibility prevents the sperm of one species from surviving in the reproductive tract or fertilizing the eggs of another species.

Postzygotic Barriers

Reproductive isolating mechanisms that act after fertilization has occurred to prevent hybrid zygotes from developing into viable, fertile adults.

Hybrid Inviability

A postzygotic barrier where incompatible genes from different parent species interact abnormally, impairing the hybrid offspring's embryonic development or post-embryonic survival.

Hybrid Sterility

A postzygotic barrier where a hybrid organism develops into a vigorous adult but cannot produce normal gametes, resulting in infertility.

Hybrid Breakdown

A postzygotic barrier where first-generation ($F_1$) hybrids are viable and fertile, but their offspring ($F_2$ or backcross generations) are feeble or sterile.

Hybridisation

The process of producing offspring by the mating and fusion of gametes from two genetically different parents, such as distinct species or varieties.

Genetic Drift

An evolutionary mechanism in which allele frequencies in a population fluctuate unpredictably from one generation to the next due to chance events, leading to a loss of genetic variation, especially in small populations.

Bottleneck Effect

A sharp reduction in genetic diversity that occurs when a sudden environmental disaster or disturbance dramatically reduces population size, leaving a surviving gene pool that does not reflect the original population.

Founder Effect

A form of genetic drift that occurs when a small group of individuals colonizes a new, isolated territory, carrying only a fraction of the genetic diversity found in the original source population.

Adaptive Radiation

The rapid evolutionary diversification of a single ancestral species into multiple distinct species, each adapted to exploit a different ecological niche or habitat under different selective pressures.

Lamarckism

The early evolutionary hypothesis proposed by Jean-Baptiste Lamarck stating that species evolve through the use and disuse of parts and the inheritance of acquired characteristics driven by a complexifying force and an adaptive force.

Descent with Modification

Charles Darwin's core evolutionary principle stating that all organisms are related through common ancestry in the remote past and have accumulated diverse adaptations over generations.

Homologous Structures

Anatomical features in different taxa that are derived from a common ancestor and share structural blueprints, which may be modified to perform different functions as a result of divergent evolution.

Analogous Structures

Anatomical features in unrelated or distantly related taxa that perform similar functions but did not evolve from a shared common ancestor, arising through convergent evolution.

Convergent Evolution

The independent evolutionary process in which distinct evolutionary lineages develop similar morphological or physiological adaptations due to exposure to similar environmental pressures and natural selection.

Gradualism

An evolutionary model proposing that speciation occurs through the continuous, steady accumulation of small variations and minor mutations over extended geological time.

Punctuated Equilibrium

An evolutionary model proposing that species undergo long periods of genetic stasis that are interrupted by rapid bursts of speciation driven by mutations in key genes over short timeframes.