Variation & Mutation

Quick revise

Continuous Variation

  • Small differences between individuals
  • Greatly affected by environment
  • e.g. height, shoe size, length of hair plotted on a line graph

Discontinuous Variation

  • Differences that are classed or categorised
  • Not greatly affected by environment
  • e.g. blood group, sex, hair colour, eye colour plotted on a bar chart or pie chart

Causes: climate, diet, lifestyle, culture, accidents

Environmental Variation

Environment affects how our inherited characteristics develop

Twins who grow up separately might become very different: e.g. fashion, taste, hair colour, build, personality, aptitudes

Genetic Variation


  • Mixing of parent information during meiosis
  • Gamete forms from a unique combination of genetic information

Siblings can have both similar and very different traits

They are mixtures of their parents, each sibling can receive different characteristics of their parents e.g. natural hair colour, eye colour, blood type


During replication, an organism’s genetic make-up (DNA) can change or mutate. Changes to genes are called mutations. Mutations can be spontaneous (they just happen). They can also happen because of:

  • Radiation
  • Chemicals, such as tar from cigarette smoke

If mutation is large then the organism will probably not survive to reproduce

If mutation is small then change might be beneficial. Offspring will flourish, doing better than others in that species. Many more offspring will inherit this beneficial mutation and will be better suited to that environment

Thus continues natural selection

Mutations may have no effect. For example, the protein that a mutated gene produces may work just as well as the protein from the non-mutated gene.

Mutations may sometimes be helpful but they are often harmful. For example, haemophilia is an inherited disorder that stops blood from clotting properly. It is caused by a mutated gene.

Genes can be switched on and off. In any one cell, only some of the full set of available genes are used. Different types of cells produce different ranges of proteins. This affects the functions they can carry out. For example, only pancreas cells switch on the gene for making the hormone insulin.

Mutations to genes can alter the production of certain proteins, or even prevent them being made by a cell.