18 Variation and Selection

18 Variation and Selection
1 Variation
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.
7. State that mutation is the way in which new alleles are formed.
8. State that ionising radiation and some chemicals increase the rate of mutation.
9. Describe gene mutation as a random change in the base sequence of DNA.
10. State that mutation, meiosis, random mating, and random fertilisation are sources of genetic variation in populations.
2 Adaptive Features
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.
3 Selection
1. Describe natural selection with reference to:
▪ Genetic variation within populations.
▪ Production of many offspring.
▪ Struggle for survival, including competition for resources.
▪ A greater chance of reproduction by individuals that are better adapted to the environment than others.
▪ These individuals pass on their alleles to the next generation.
2. Describe selective breeding with reference to:
▪ Selection by humans of individuals with desirable features.
▪ Crossing these individuals to produce the next generation.
▪ Selection of offspring showing the desirable features.
3. 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.
4. Describe adaptation as the process, resulting from natural selection, by which populations become more suited to their environment over many generations.
5. Describe the development of strains of antibiotic-resistant bacteria as an example of natural selection.
6. Outline the differences between natural and artificial selection.

18 Variation and Selection

1 Variation

2 Adaptive Features

3 Selection