Variation

Definition

• Variation = all the differences in the characteristics of individuals in a population.

Causes of Variation

1. Genetic causes (inherited alleles)

   • Different alleles inherited from parents.

   • Examples:

     • Hair color (red, blonde, dark).

     • Eye color (blue, brown).

2. Environmental causes

   • Conditions in which an organism develops.

   • Examples:

     • Flower color depending on soil pH.

     • Language in humans.

3. Combination of genes and environment

   • Both genetic factors and environmental influences.

   • Example:

     • Height in humans: alleles influence potential height, but enough calcium in diet is needed for full bone development.

Mutations

• Mutation = random change to DNA.

• Happen all the time.

• Most mutations:

  • No effect on phenotype.

• Some mutations:

  • Influence phenotype (e.g. alleles for tallness if diet is suitable).

• Very small number:

  • Determine phenotype directly (e.g. eye colour).

Beneficial Phenotypes

• Rarely, a mutation → new phenotype.

• If environment changes, the new phenotype can be beneficial → spread quickly in population.

• Example:

  • 1950s, virus killed 99% of wild rabbits in the UK.

  • Mutation occurred → rabbits became resistant.

  • Beneficial phenotype spread → now widespread.

✅ Key takeaways:

• Variation comes from genetics, environment, or both.

• Mutations create genetic variation.