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.