18. Variation and Selection

• 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

• 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 (Hb^S Hb^A) 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 (Teaching of human inherited conditions should be done with sensitivity at all times.)

• 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

• 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

• 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

• 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