18 Variation and Selection
(Core / Extended)

18.1 Variation
What you need to know:

1. Describe variation as differences between individuals of the same species
   
2. State that continuous variation results in a range of phenotypes between two extremes; examples include body length and body mass
   
3. State that discontinuous variation results in a limited number of phenotypes with no intermediates; examples include ABO blood groups, seed shape in peas and seed colour in peas
   
4. State that discontinuous variation is usually caused by genes only and continuous variation is caused by both genes and the environment
   
5. Investigate and describe examples of continuous and discontinuous variation 6 Describe mutation as genetic change
6. Describe gene mutation as a random change in the base sequence of DNA
   
7. State that mutation is the way in which new alleles are formed 
   
8. State that mutation, meiosis, random mating and random fertilisation are sources of genetic variation in populations 
   
9. State that ionising radiation and some chemicals increase the rate of mutation​
   

Videos: Variation and Selection

Videos: ​​Variation and Mutation

Videos: DNA Mutation

18.2 Adaptive Features
What you need to know:

1. Describe an adaptive feature as an inherited feature that helps an organism to survive and reproduce in its environment
   
2. Interpret images or other information about a species to describe its adaptive features
3. Explain the adaptive features of hydrophytes and xerophytes to their environments
   

Videos: Adaptation

Videos: Xerophytic Adaptation

Videos: Plant Adaptation: Xerophytic Hydrophytic (Mesophytic) 

18.3 Selection
What you need to know:

1. Describe natural selection with reference to: (a) genetic variation within populations (b) production of many offspring (c) struggle for survival, including competition for resources (d) a greater chance of reproduction by individuals that are better adapted to the environment than others (e) these individuals pass on their alleles to the next generation
2. Describe adaptation as the process, resulting from natural selection, by which populations become more suited to their environment over many generations
3. Describe the development of strains of antibiotic resistant bacteria as an example of natural selection​
4. Describe selective breeding with reference to: (a) selection by humans of individuals with desirable features (b) crossing these individuals to produce the next generation (c) selection of offspring showing the desirable features
5. Outline how selective breeding by artificial selection is carried out over many generations to improve crop plants and domesticated animals and apply this to given contexts
6. Outline the differences between natural and artificial selection 

Videos: Natural Selection

Videos: Antibiotic Resistance

Videos: Selective Breeding

EXAMPLE QUESTIONS

Videos: Inheritance and Genetic Crosses Exam Questions