Sources Of Inherited Variation

• Mutation


  A change in the DNA sequence in a chromosome
• Types of mutations


  • Deletions
  • Translocation
  • Duplication
  • Inversion
• In most cases, the DNA of an organism will remain the same throughout its life
• When mutations do occur, they provide a continuous supply of NEW genetic information
• Causes of mutations


  • Environmental factors (chemicals or radiation)
  • Errors that arise when cells use or make copies of the DNA molecules
• Neutral mutation


  Has no immediate effect on an individual's fitness (an organism's reproductive success)
• Harmful mutation


  Reduces an individual's fitness. These mutations are selected against and therefore do not accumulate over the generations
• Beneficial mutation


  Gives an individual a selective advantage (enhances their fitness). These mutations are selected for and may accumulate over the generations, even though they are rare
• Asexual reproduction


  The production of offspring from a single parent. Offspring receives an identical copy of its parent's DNA
• Sexual reproduction


  The production of offspring by the union of sex cells from two different parents. Offspring inherit a combination of genes from both parents
• Sexually-reproducing species have two copies of EACH gene. Each copy may be identical OR different. Both parents contribute one copy of each gene to the offspring
• The assortment of genes that an offspring inherits from either parent is determined randomly. Each sibling therefore has a unique combination of genes
• The GREATER the number of genes a species has, the larger the number of combinations and the greater the genetic variability of the species as a whole
• Sexually reproducing species choose different mates. Each combination of parents will give rise to different combinations of genes and traits in the NEXT generation
• Darwinian evolution


  Inherited characteristics, population variability, source of new variation, natural selection, evolutionary change
• Genetic mechanisms


  Inherited characteristics are determined by genes, individuals of the same species differ from one another due to different combinations of genes, new traits can arise when genes become mutated, some genes determine traits that make the individual better suited for survival and reproductive success, evolution is the change in the population's gene pool over many generations
• Mutation

  A change in the DNA sequence in a chromosome
• Types of mutations

  • Deletions
  • Translocation
  • Duplication
  • Inversion
• In most cases, the DNA of an organism will remain the same throughout its life
• When mutations do occur, they provide a continuous supply of NEW genetic information
• Causes of mutations

  • Environmental factors (chemicals or radiation)
  • Errors that arise when cells use or make copies of the DNA molecules
• Neutral Mutation

  Has no immediate effect on an individual's fitness (an organism's reproductive success)
• Harmful Mutation

  Reduces an individual's fitness. These mutations are selected against and therefore do not accumulate over the generations
• Beneficial Mutation

  Gives an individual a selective advantage (enhances their fitness). These mutations are selected for and may accumulate over the generations, even though they are rare
• Asexual Reproduction

  The production of offspring from a single parent. Offspring receives an identical copy of its parent's DNA
• Sexual Reproduction

  The production of offspring by the union of sex cells from two different parents. Offspring inherit a combination of genes from both parents
• Sexually-reproducing species have two copies of EACH gene. Each copy may be identical OR different. Both parents contribute one copy of each gene to the offspring
• The assortment of genes that an offspring inherits from either parent is determined randomly. Each sibling therefore has a unique combination of genes
• The GREATER the number of genes a species has, the larger the number of combinations and the greater the genetic variability of the species as a whole
• Sexually reproducing species choose different mates. Each combination of parents will give rise to different combinations of genes and traits in the NEXT generation
• Inherited characteristics


  Determined by genes. Organisms typically possess thousands of different genes
• Population variability


  Individuals of the same species differ from one another, in part because they possess different combinations of genes. The genetic makeup of all individuals within a population is called the population's gene pool
• Source of new variation

  New traits can arise when genes become mutated
• Natural selection


  Some genes determine traits that make the individual better suited for survival and reproductive success. Individuals with these traits produce more offspring, some of which will inherit these advantageous genes
• Evolutionary change


  Over many generations, individuals carrying the genes that determine the most favourable traits for survival and reproductive success will become more common in the population
• Divergent Evolution (macroevolution)


  A process of developing two or more species from a common ancestor over time. The accumulation of differences between groups is usually a result of diffusion of the same species to different and isolated environments, which BLOCKS the gene flow among the distinct populations.
• Burgess Shale


  • One of the most important fossil discoveries in the world (evidence of the Cambrian explosion), contains beautifully preserved 515-million-year-old fossils of marine life. The great diversity is evidence of divergent evolution.
• Adaptive Radiation (microevolution)


  A type of divergent evolution in which organisms diversify rapidly (500 000 years or more) from an ancestral species into a multitude of NEW forms, particularly when a change in the environment makes new resources available, creates new challenges, or opens new environmental niches.
• Allopatric Speciation


  A result of divergent evolution where a physical barrier separates a single interbreeding population into two or more groups that are isolated from each other, leading to independent evolution and eventual reproductive isolation.
• Allopatric Speciation


  1. Physical barrier separates population

  2. Natural selection works on separated groups independently

  3. Accumulated differences lead to reproductive isolation