Variation in populations

Individuals in a population are not usually identical: they differ in characteristics such as height or blood group. These differences are called variation. A population is a group of individuals of the same species living in the same area.

Individuals of the same species usually have extensive genetic variation: they inherit different versions of genetic material from their parents. These genetic differences can produce differences in characteristics. For example, a person's blood group is determined by inherited genetic material.

Characteristics can also differ because individuals experience different environmental conditions as they develop. For example, a scar can result from an injury rather than from an inherited genetic difference.

A person's observable characteristics are called their phenotype. Some aspects of phenotype are influenced by both inherited genetic differences and the environment. For example, height is influenced by inherited genetic material, but nutrition during growth also affects how tall a person becomes.

Mutations as a source of genetic variation

A mutation is a change in genetic material. Mutations occur continuously and create genetic variants: different versions of genetic material. They are the ultimate source of these variants, even though a variant found in an individual may have been inherited from a parent rather than produced by a new mutation.

A mutation can contribute to genetic differences between individuals if the resulting variant is inherited. Not every mutation is passed on to offspring.

Effects of genetic variants on phenotype

An individual’s phenotype is its observable characteristics. Most mutations have no effect on phenotype. Some variants influence a characteristic, often alongside environmental factors. For example, a variant may affect a characteristic without being the only cause of the outcome.

Very few variants determine a characteristic on their own. Very rarely, a mutation leads to a new phenotype.

Selection of advantageous new phenotypes

A phenotype is an observable characteristic of an organism. A new phenotype can be inherited if it is associated with a genetic variant that can be passed from parents to offspring.

If the environment changes, a phenotype may become advantageous because it makes individuals better suited to the new conditions. Individuals with that phenotype may be more likely to survive and reproduce than others in the population. When they reproduce, they can pass the associated genetic variant to their offspring, which may then show the same phenotype.

Over generations, the genetic variant and its associated phenotype can become more common in the population. This process is called natural selection. If the advantageous phenotype spreads through the population over relatively few generations, the species can change relatively rapidly.