Chapter 6: Variation

  • All living things exhibit variation.
  • Variation is a condition where members of the same species differ in one or more traits.
  • The two types of variation are continuous and discontinuous variation.
  • In continuous variation, members of a population vary across a range.
  • Examples of continuous variation are height and weight of humans.
  • In discontinuous variation, the members of a population are grouped into a few distinct groups for a particular character.
  • An example of discontinuous variation is human blood groups.
  • Variation is affected by genetic and environmental factors.
  • Examples of genetic factors are crossing over, independent assortment, random fertilisation and mutation.
  • Examples of environmental factors are climate and nutrition.
  • Mutation is a spontaneous or induced change in the DNA of genetic material.
  • Any descendants of an individual with a mutation showing the new characteristics are known as mutants.
  • Mutation causes discontinuous variation in a population.
  • Mutation can be classified either as a gene or chromosomal mutation.
  • Chromosomal mutation involves a change in either the structure of the chromosome that is the arrangement of the genes or in the number of chromosomes.
  • Down's syndrome is a genetic disorder caused by chromosomal mutation.
  • A gene mutation is also known as point mutation.
  • A gene mutation is caused by a change at a single locus on a chromosome involving one nucleotide base.
  • Gene mutations cause disorders like haemophilia, colour blindness, sickle-cell anaemia and albinism.
  • Mutagens are agents which cause mutation.
  • Examples of mutagens are ultraviolet radiation and chemicals.
  • Variation among organisms of the same species is important for the survival of the species. It equips a species to fight the odds in an everchanging environment.


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