Differences in the characteristics of individuals in a population is…

The idea

Variation means the differences in characteristics between individuals of the same population. It arises from three possible sources. Genetic causes come from the alleles inherited from parents; for example, eye colour is largely genetic. Environmental causes come from conditions during development and life, such as diet, exercise, temperature or light; for example, a plant grown in shade may be tall and thin. Many characteristics result from a combination of both, such as human height or body mass, where genes set a potential range and the environment influences where an individual falls within it. When answering, identify the characteristic, then explain which cause or causes are involved and why. Avoid saying a characteristic is only genetic or only environmental unless the evidence supports it.

What earns the marks

• Defines variation as differences in characteristics between individuals in a population.
• Identifies genetic causes as differences in the alleles inherited from parents.
• Identifies environmental causes as differences in the conditions in which organisms develop or live.
• Explains that many characteristics are influenced by a combination of genetic and environmental factors.
• Uses a named example to illustrate each cause or a combined cause.
• Distinguishes between the source of the variation and the characteristic itself.

Common mistakes and how to put them right

• Stating that all variation is genetic.

  Put it right by explaining that environmental conditions can also cause differences.

• Confusing a gene with an allele.

  Put it right by using allele for a version of a gene.

• Claiming that a single characteristic is always caused only by genes or only by the environment.

  Put it right by recognising that many show combined causation.

Exam tips

• When given data about a characteristic, look for evidence that separates genetic from environmental effects, such as identical twins raised apart or clones grown in different conditions.
• Use the phrase 'combination of genes and the environment' when both factors contribute, and support it with a specific example.
• Check that each cause you name is linked to the characteristic in the question, not just listed generally.