Chapter 23

• Population genetics


  The study of genes and genotypes in a population
• Population


  • Groups of interacting individuals of the same species that occupy the same environment/area at the same time
• Population genetics studies the genetic makeup and variations of populations over time
• Individual variation abounds in populations
• Not all of this variation is heritable
• Only the genetic component of variation is relevant to natural selection
• Gene pool


  All of the alleles for every gene in a given population
• Population genetics studies the genetic variation within the gene pool and how variation changes from one generation to the next
• Individuals that reproduce contribute to the gene pool of the next generation
• Populations change from one generation to the next
• Some of the genetic changes involve adaptation, in which a population becomes better suited to its environment, making it more likely to survive and reproduce
• Microevolution


  The change in the genetic makeup (gene pool) of a population from generation to generation
• Causes of microevolution


  • Introduction of new genetic variation such as mutations to alleles and gene duplication
  • Evolutionary mechanisms that alter the prevalence of an allele or genotype in a population (natural selection, genetic drift, and nonrandom mating)
• Evolutionary mechanisms that alter the prevalence of a given allele or genotype

  • Natural selection
  • Sexual selection
  • Genetic drift
  • Migration
  • Nonrandom mating
• Natural selection


  The process in which individuals with certain heritable traits tend to survive and reproduce at higher rates than those without those traits
• Types of natural selection

  • Directional selection
  • Balancing selection
• Sexual selection


  A form of natural selection that results from individuals with certain traits being more likely to successfully reproduce than others
• Types of sexual selection

  • Intrasexual selection (between members of the same sex)
  • Intersexual selection (between members of the opposite sex)
• Genetic drift


  The genetic fluctuation in allele frequencies due to random chance from one generation to the next
• Examples of genetic drift

  • Bottleneck effect
  • Founder effect
• Bottleneck effect


  A sudden change in the environment may drastically reduce the size of a population, killing members unselectively, resulting in a small surviving population that is unlikely to be representative of the original population
• Founder effect


  When a small group of individuals becomes separated or isolated from a larger population and form a new population in a new location, the new population is unlikely to be representative of the original population
• Migration


  The movement of individuals in or out of a population, resulting in genetic exchange due to the migration of fertile individuals or gametes between populations