lesson 4

• Hardy-Weinberg principle


  A principle stating that the genetic variation in a population will remain constant from one generation to the next in the absence of disturbing factors
• Hardy-Weinberg equilibrium


  • When mating is random in a large population with no disruptive circumstances, the law predicts that both genotype and allele frequencies will remain constant because they are in equilibrium
• Disturbances to the Hardy-Weinberg equilibrium

  • Mutations
  • Natural selection
  • Nonrandom mating
  • Genetic drift
  • Gene flow
• Because these disruptive forces are common in nature, the Hardy-Weinberg equilibrium rarely apply in nature
• The Hardy-Weinberg equilibrium describes an idealized state, and the genetic variation in nature can be measured as changes from this equilibrium state
• The Hardy-Weinberg equation can still be applied
• Descent of Modifications


  A theory proposed by Charles Darwin that explains how species change over time through the process of natural selection
• Evolutionary Thought


  The scientific study of how species have changed over time and how new species arise
• Population will remain constant from one generation to the next in the absence of disturbing factors.
• Hardy-Weinberg principle


  When mating is random in a large population with no disruptive circumstances, the law predicts that both genotype and allele frequencies will remain constant because they are in equilibrium.
• Disturbances to the Hardy-Weinberg equilibrium

  • Mutations
  • Natural selection
  • Nonrandom mating
  • Genetic drift
  • Gene flow
• Because these disruptive forces are common in nature, the Hardy-Weinberg equilibrium rarely apply in nature.
• The Hardy-Weinberg equilibrium describes an idealized state, and the genetic variation in nature can be measured as changes from this equilibrium state.
• The Hardy-Weinberg equation can still be applied to make predictions on possible genetic changes.
• Descent with modifications


  Refers to the passing of traits from parent organisms to their offspring. This passing of traits is called heredity, and the basic unit of heredity is the gene.
• Evolution


  The idea that species change over time, and give rise to new species, and share a common ancestor.
• Selection (in biology)


  The preferential survival and reproduction (or preferential elimination) of individuals with certain genotypes (genetic compositions), by means of natural or artificial controlling factors.
• Types of selection


  • Natural selection
  • Artificial selection
• Natural selection


  The process in nature by which, according to Darwin's theory of evolution, only the organisms best adapted to their environment tend to survive and transmit their genetic characters in increasing numbers to succeeding generations while those less adapted tend to be eliminated.
• Artificial selection


  A form of selection in which humans actively choose which traits should be passed onto a plant or animal's offspring. Unlike natural selection, the process is not random but is controlled.
• Speciation


  The formation of new and distinct species in the course of evolution.
• Ways speciation can take place

  • Sympatric speciation
  • Allopatric speciation
• Sympatric speciation


  Occurs when a single species develop into two distinct species as a result of reproductive isolation, despite living in the same geographical area.
• Allopatric speciation


  Occurs when a species gets split into two geographically isolated populations. The isolated populations may then be subjected to slightly different conditions and therefore selection pressures. Genetic drift and mutations may also contribute to differences in each population.
• Factors contributing to the formation of new species

  • Isolation
  • Genetic drift: bottleneck effect & founder effect
  • Hybridization
  • Adaptive radiation
• Lamarck's theory


  If an organism changes during life in order to adapt to its environment, those changes are passed on to its offspring. He said that change is made by what the organisms want or need.
• Lamarck's theory


  Differs from Darwin's theory of natural selection and survival of the fittest
• Evidence supporting the Theory of Evolution

  • Paleontology
  • Geographical distribution
  • Comparative anatomy
  • Comparative embryology
  • Biochemistry
  • DNA homology