Variation and Evolution

GCSE Biology · Inheritance

Variation

Differences between individuals, caused by:

Genetic (alleles inherited),
Environmental (e.g. diet, scars),
or both (e.g. height).

Mutations are random changes to DNA — the source of new alleles; most have no effect, a few are harmful or beneficial.

Natural selection (Darwin)

1. Individuals show variation.

2. Those with advantageous characteristics are more likely to survive and reproduce.

3. They pass on the beneficial alleles.

4. Over many generations the species evolves.

Example: antibiotic-resistant bacteria, peppered moths.

Evidence for evolution

Fossils (record of change over time).
Antibiotic resistance in bacteria (evolution we can observe).

Selective breeding (artificial selection)

Humans choose organisms with desired traits to breed (e.g. high-yield crops, docile animals). Risk: reduced gene pool → inbreeding problems.

Genetic engineering

Transferring genes from one organism to another (e.g. insulin-producing bacteria, pest-resistant crops). Benefits vs ethical concerns.

Exam tip

Structure natural-selection answers as: variation → survival of the fittest → reproduction → alleles passed on → species changes. Mutations create the variation.