LEARNING OBJECTIVES
By the end of this chapter, you should be able to:
- compare variation types
- explain mutation
- identify adaptations
- explain natural selection
- compare natural and artificial selection
THE BIG IDEA
How differences arise and populations change across generations.
This chapter builds each process from its structures, inputs and outputs. Follow the connections rather than memorising isolated facts, then use precise biological terms when explaining cause and effect.
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
- Height and mass are continuous; ABO group and pea seed shape are discontinuous.
- 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
- Xerophytes may have reduced leaves, thick cuticle, sunken stomata and water storage.
- 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
- Antibiotics select resistant bacteria; they do not create the mutation.
- 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.
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.