Variation
Two kinds of variation
- Variation is the differences between individuals of the same species.
- continuous — a smooth range between two extremes (e.g. height, mass).
- discontinuous — a few separate groups with nothing in between (e.g. ABO blood groups).
Practice
Which is an example of continuous variation?
Height varies smoothly across a range (continuous); blood group and seed shape fall into separate groups (discontinuous).
What causes it
- Discontinuous variation is usually caused by genes only.
- Continuous variation is caused by both genes and the environment (e.g. height depends on genes and diet).
Practice
Continuous variation is caused by:
Continuous variation (e.g. height) is influenced by genes and the environment; discontinuous variation is usually genes only.
Mutation
- A mutation is a genetic change — the way new alleles are made, so the source of all variation.
- (Supplement) A gene mutation is a random change in the DNA base sequence.
- Ionising radiation (e.g. X-rays) and some chemicals raise the mutation rate.
Practice
A mutation is important because it:
Mutations create new alleles, the original source of genetic variation; radiation and some chemicals raise the rate.
You've got it
Key idea
- continuous variation = a smooth range (genes + environment); discontinuous = separate groups (genes only)
- mutation makes new alleles — the source of all variation
- radiation and some chemicals raise the mutation rate