Variation: Differences in the characteristics of individuals in a population is called variation and may be due to differences in:

The idea

Variation means the differences in characteristics between individuals in a population. It arises from two broad sources. Genetic causes include differences in the alleles inherited, new alleles formed by mutation, and the random combination of parental alleles during sexual reproduction. Environmental causes include diet, exercise, temperature, light, nutrient availability and lifestyle factors. Many characteristics, such as human height or plant leaf size, are influenced by both genes and environment. Some variation is discontinuous, falling into distinct categories such as blood group or eye colour, while other variation is continuous, showing a range of values such as height or mass. A population with more genetic variation is more likely to survive a change in the environment, because some individuals may have advantageous characteristics.

What earns the marks

• Defines variation as differences in characteristics between individuals within a population.
• Identifies genetic causes of variation, including differences in alleles inherited, mutation and the random combination of alleles in sexual reproduction.
• Identifies environmental causes of variation, including diet, exercise, temperature, light and other lifestyle or habitat factors.
• Explains that many characteristics result from both genetic and environmental influences acting together.
• Distinguishes discontinuous variation, which falls into distinct categories, from continuous variation, which shows a range of values.
• Links genetic variation in a population to increased chance of survival when the environment changes.

Common mistakes and how to put them right

• Listing only genetic causes.

  Put it right by including environmental factors such as diet, exercise and temperature.

• Calling any difference between species variation.

  Put it right by stating that variation refers to differences between individuals of the same population or species.

• Assuming continuous variation is always genetic.

  Put it right by explaining that continuous characteristics such as height are usually affected by both genes and environment.

Exam tips

• Structure answers by separating genetic causes from environmental causes, then give one example of each.
• Use the terms continuous and discontinuous correctly, and support each with a named example.
• When asked to explain, link the cause of variation to its effect on the individual or population rather than just naming factors.