chapter 9 definitions

• Accumulation


  The process of alleles or traits gradually becoming more common over generations
• Adaptive evolution


  Changes in a population of organisms that make that population better adapted to its environment over time
• Adaptive radiation


  The process by which a species rapidly diversifies into many taxa with differing adaptations; it can be triggered by many factors, such as the emergence of reproductive barriers within a population, changes in the availability of resources, new challenges or new opportunities; it is a type of divergent evolution
• Allopatric speciation


  Speciation that occurs due to physical or geographic isolation
• Artificial selection (selective breeding)


  The intentional breeding or reproduction by humans of individuals with desirable traits, resulting in changes in allele frequencies in gene pools over time; the traits are beneficial to humans
• Biological fitness


  The capacity of an individual to survive and produce viable, fertile offspring
• Biological species concept


  A definition of species based on whether members can interbreed to produce fertile offspring
• Descent with modification


  Darwin's terminology for the way life today has descended and evolved from common ancestors that were generally different from their modern descendants
• Divergent evolution


  A process whereby related species evolve new traits over time after living in different habitats, becoming increasingly different from their common ancestor and from one another, giving rise to new species
• Evolution


  The process of cumulative, gradual, heritable change in a population of organisms that occurs over many generations and a relatively long time
• Founder effect


  A random reduction in a population that occurs when a few individuals become isolated from a larger population and form a new population that does not carry all the alleles that were present in the original population
• Gene flow


  The transfer of alleles that results from emigration, immigration and migration of individuals between populations
• Gene pool


  A collection of all the alleles for all the genes in the reproducing members of a population at a given time; it is the genetic reservoir from which a population can obtain its traits
• Genetic drift


  A change in the gene pool of a population as a result of chance; it usually occurs more noticeably in small populations
• Hybrid offspring


  Offspring from parents of two different species
• Inheritable


  Capable of being passed on to the next generation
• Isolating mechanism


  A mechanism that prevents organisms from mating or producing viable offspring
• Macro-evolution


  The evolution of new groups of organisms comprising many related species through multiple speciation events; includes adaptive radiations
• Mass extinction


  Extinction of many species over a relatively short (geological) period of time
• Micro-evolution


  Change in the gene pool below species level; any small-scale change in the gene pool of a population
• Modern synthesis


  The theory of evolution incorporating our current understanding of how traits are inherited
• Morphological species concept


  Definition of a species using measurable anatomical criteria and characteristics
• Mutation


  A permanent change in the DNA sequence of a gene; a source of new alleles in a population's gene pool; the process of generating a mutation
• Natural selection


  Occurs when selection pressures in the environment confer a selective advantage on a specific phenotype that enhances its survival and reproduction. It is a process in which individuals that have certain inherited traits are more likely to survive and reproduce at higher rates than other individuals because of those traits. It can cause changes in a population's allele frequencies (gene pool) and therefore is a mechanism for evolution
• Population


  A group of individuals of the same species that live in the same area and interbreed, producing fertile offspring
• Post-reproductive isolating mechanism


  A mechanism that prevents fertilisation occurring or an embryo developing into viable offspring if fertilisation does occur
• Pre-reproductive isolating mechanism


  A mechanism that prevents organisms from being able to interact to reproduce
• Reproductive isolation


  When a single population becomes two separate populations that are unable to interbreed due to physical, biological or behavioural barriers
• Selection pressure


  A factor that influences the survival of an individual within a population
• Sexual dimorphism


  Different morphologies (often in shape or size) between males and females of a species
• Sexual selection


  A selection process that occurs between males or between females in a population for an inherited trait that assists in copulation or the winning of a mate
• Speciation


  The evolution of one or more new species from an ancestral species. A population is considered a new species when it can no longer interbreed with the ancestral species.
• Species


  A group of similar organisms capable of breeding and exchanging genes with one another and whose offspring are capable of doing the same
• Sympatric speciation


  Speciation that occurs without physical or geographic isolation
• Theory of evolution


  States that all organisms have developed from previous organisms and that all living things have a common ancestor in some initial form of primitive life. It also states that all organisms are fundamentally similar because their basic chemistry was inherited from this very first organism.
• Variable trait


  A trait that varies in the population due to differences in alleles carried by different individuals
• Variation


  The diversity of genetic and phenotypic traits within and between populations