Chapter Summary

Focus of the chapter:

  • Definitions of populations: demes, species
  • Hardy-Weinberg and the application of population genetics to evolution
  • Mutation and the introduction of new alleles into populations
  • Genetics and natural selection
  • Examples of natural selection: peppered moth and sickle-cell anemia
  • Population genetics: gene flow and gene drift

Species is the term that describes all members of a population capable of breeding and producing fertile offspring that are reproductively isolated from other such groups. Within a species are demes, or members that actually produce offspring.

The Hardy-Weinberg equilibrium is the recognition that under certain circumstances, genotype frequencies remain stable over generations. Scientists use the resulting formula to determine if change is occurring within a population.

New genetic information is introduced through mutation. Mutation can occur in several ways, one of which is through incorrect base pairing (point mutations). Point mutations affect only a small portion of the genome, whereas other types of mutations may affect larger segments.

Natural selection can occur in several patterns. Directional selection favors one extreme form of a trait; stabilizing selection favors the average version of a trait. Disruptive selection favors both extremes and produces a bimodal pattern.

Sickle-cell anemia is perhaps the best-known example of natural selection in humans and highlights the relationships among culture, genetics, and disease.

Gene drift can occur when a small subsample from a larger population becomes isolated. Gene flow happens when genetic information is exchanged between groups. Study of these mechanisms of evolution can lend insight into the spread of humans throughout the world.