Chapter 23 Syllabus

23.1 Variation
- Definition and importance

23.1.1 Continuous and discontinuous variation
- Definition, differences and examples

23.1.2 Source
i) Genetic
- Sexual reproduction
- Random assortment of homologous chromosomes during meiosis
- Crossing-over, chromosome mutation, gene mutation, polygenes, dominant and recessive gene/alleles

ii) Environment
- Factors and influences

23.2 Selection
- Definition, description, importance and examples

23.2.1 Natural Selection
- Stabilising selection
- Directional selection
- Disruptive selection
- Sexual selection
- Polymorphism

23.2.2 Artificial Selection
- Breeding of farm animals and crop plants
- Controlled/selective breeding (inbreeding, outbreeding)
- Human and animal sperm banks

23.3 Speciation
- Definition, description, importance and examples

23.3.1 Concept of species
- Problems in defining species

23.3.2 Speciation process
- Formation of new species
- Isolation, genetic drift, hybridisation and adaptive radiation

23.4 Evolution
23.4.1 Lamarck's Theory
-Theory and examples

23.4.2 Darwin-Wallace's Theory
- Theory and examples

23.4.3 Evidence supporting theory of evolution
- Paleontology
- Geographical distribution
- Comparative anatomy
- Comparative embryology
- Biochemistry
- DNA homology