18. Variation and selection
18.1 Variation
Core
Define variation as differences between individuals of the same species
Distinguish between phenotypic variation and genetic variation
State that continuous variation results in a range of phenotypes between two extremes, e.g. height in humans
State that discontinuous variation results in a limited number of phenotypes with no intermediates, e.g. tongue rolling
Record and present the results of investigations into continuous and discontinuous variation
Define mutation as genetic change • State that mutation is the way in which new alleles are formed
State that ionising radiation and some chemicals increase the rate of mutation
Supplement
State that phenotypic variation is caused by both genetic and environmental factors
State that discontinuous variation is mostly caused by genes alone, e.g. A, B, AB and O blood groups in humans
Define gene mutation as a change in the base sequence of DNA
Describe the symptoms of sickle cell anaemia
Explain how a change in the base sequence of the gene for haemoglobin results in abnormal haemoglobin and sickle-shaped red blood cells
Use genetic diagrams to show how sickle cell anaemia is inherited
State that people who are heterozygous (HbS HbA ) for the sickle cell allele have a resistance to malaria
Explain the distribution of the sickle cell allele in human populations with reference to the distribution of malaria.
Types of variation
Mutations
Sickle cell anaemia
Explaining the tree of life
Topic overview
18.2 Adaptive features
Core
Define adaptive feature as an inherited feature that helps an organism to survive and reproduce in its environment
Interpret images or other information about a species to describe its adaptive features
Supplement
Define adaptive feature as the inherited functional features of an organism that increase its fitness
Define fitness as the probability of an organism surviving and reproducing in the environment in which it is found
Explain the adaptive features of hydrophytes and xerophytes to their environments
Adaptations of a polar bear.
Adaptive features
Adaptations of a camel
Hydrophytes and Xerophytes
18.3 Selection
Core
Describe natural selection with reference to:
– variation within populations
– production of many offspring
– competition for resources
– struggle for survival
– reproduction by individuals that are better adapted to the environment than others
– passing on of their alleles to the next generation
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
Supplement
Describe evolution as the change in adaptive features of a population over time as the result of natural selection
Define the process of adaptation as the process, resulting from natural selection, by which populations become more suited to their environment over many generations
Describe the development of strains of antibiotic resistant bacteria as an example of evolution by natural selection
State the differences between natural and artificial selection
Outline how selective breeding by artificial selection is carried out over many generations to improve crop plants and domesticated animals
Natural selection
How did Darwin come up with his theory?
Selective Breeding 1
Selective breeding 2
Antibiotic resistance
Variation, inheritance and evolution
Topic summary