17 Selection and evolution
In 1858, Charles Darwin and Alfred Russel Wallace proposed a theory of natural selection to account for the
evolution of
... [Show More] species. A year later, Darwin published On the Origin of Species, providing evidence for the way in
which aspects of the environment act as agents of selection and determine which phenotypic forms survive and
which do not. The individuals best adapted to the prevailing conditions are most likely to succeed in the ‘struggle
for existence’.
17.1 Variation Learning outcomes
Candidates should be able to:
1 explain, with examples, that phenotypic variation is due to
genetic factors or environmental factors or a combination of
genetic and environmental factors
2 explain what is meant by discontinuous variation and
continuous variation
3 explain the genetic basis of discontinuous variation and
continuous variation
4 use the t-test to compare the means of two different samples
(the formula for the t-test will be provided, as shown in the
Mathematical requirements)
17.2 Natural and artificial
selection
Learning outcomes
Candidates should be able to:
1 explain that natural selection occurs because populations
have the capacity to produce many offspring that compete for
resources; in the ‘struggle for existence’, individuals that are
best adapted are most likely to survive to reproduce and pass on
their alleles to the next generation
2 explain how environmental factors can act as stabilising,
disruptive and directional forces of natural selection
3 explain how selection, the founder effect and genetic drift,
including the bottleneck effect, may affect allele frequencies in
populations
4 outline how bacteria become resistant to antibiotics as an
example of natural selection
5 use the Hardy–Weinberg principle to calculate allele and
genotype frequencies in populations and state the conditions
when this principle can be applied (the two equations for the
Hardy–Weinberg principle will be provided, as shown in the
Mathematical requirements)
6 describe the principles of selective breeding (artificial selection)
7 outline the following examples of selective breeding:
• the introduction of disease resistance to varieties of wheat
and rice
• inbreeding and hybridisation to produce vigorous, uniform
varieties of maize
• improving the milk yield of dairy cattle
17.3 Evolution Learning outcomes
Candidates should be able to:
1 outline the theory of evolution as a process leading to the
formation of new species from pre-existing species over time, as
a result of changes to gene pools from generation to generation
2 discuss how DNA sequence data can show evolutionary
relationships between species
3 explain how speciation may occur as a result of genetic isolation
by:
• geographical separation (allopatric speciation)
• ecological and behavioural separation (sympatric
speciation [Show Less]