LEARNING OBJECTIVES
What you will be able to do
- compare variation types
- explain mutation
- identify adaptations
- explain natural selection
- compare natural and artificial selection
AT A GLANCE
INTRODUCTION · THE BIG IDEA
How differences arise and populations change across generations.
Individuals of one species are not identical. Genetic and environmental causes create variation on which natural or artificial selection can act.
A complete selection explanation must connect inherited variation, selection pressure, unequal reproductive success and changing allele frequencies across generations.
SECTION 01
Variation and mutation
Continuous variation forms a range and is influenced by genes and environment; discontinuous variation has distinct categories and is usually genetic.
DETAILED EXPLANATION
- A gene mutation is a random DNA base-sequence change that can create a new allele.
- Ionising radiation and some chemicals increase mutation rate.
- Mutation, meiosis, random mating and random fertilisation generate variation.
SECTION 02
Adaptive features
An adaptation is an inherited feature improving survival and reproduction in a particular environment.
DETAILED EXPLANATION
- Hydrophytes may have floating leaves, upper stomata, air spaces and reduced support tissue.
SECTION 03
Selection
Populations vary and overproduce. Competition means better-adapted individuals reproduce more and pass on useful alleles, changing allele frequency over generations.
DETAILED EXPLANATION
- Selective breeding repeatedly crosses parents and selects offspring with desired traits.
- Natural selection follows environmental pressure; artificial selection follows human priorities and may reduce diversity.
STEP-BY-STEP EXAM EXAMPLE
Explaining natural selection in a dry habitat
- Individuals vary in a heritable feature affecting water conservation.
- Dry conditions create selection pressure.
- Individuals conserving more water are more likely to survive and reproduce.
- They pass their advantageous alleles to offspring, increasing their frequency.
Answer: Over generations, the population becomes better adapted to dry conditions.
QUICK CHAPTER SUMMARY
The ideas to carry forward
- Variation has different patterns and causes.
- Mutation creates alleles.
- Adaptations are inherited advantages.
- Selection changes populations.
- Artificial selection serves human choices.
QUICK REVISION CHECKLIST
Can you do each of these without your notes?
- compare variation types
- explain mutation
- identify adaptations
- explain natural selection
- compare natural and artificial selection