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Biology Unit 4
Topic 5: On the wild side
21. Describe how evolution (a change in the allele
frequency) can come about through gene mutation
and natural selection.
The theory of evolution is about how and why organisms have changed over time. What actually
changes is allele frequency (the relative frequency of a particular allele in a population). New alleles
arise from random changes in the DNA which makes up genes (gene mutations) and create variation
within the population. Once a gene mutation has appeared it is acted upon by the selection pressures
in the environment.
Mutations are changes in the DNA structure. These changes may be tiny, such as a change in a single
base pair, or they may involve the obliteration or duplication of an entire chromosome. Some
mutations have no effect at all on the phenotype, while others have severe or even lethal effects.
Mutations can increase the gene pool of a population by increasing the number of different alleles
available. The relative frequency of a particular allele in a population is the allele frequency. If a
mutation results in an advantageous feature, the frequency of that allele in the population will be
selected for and so increase in frequency. If the mutation is disadvantageous, natural selection will
usually result in its removal from the gene pool. Changes in allele frequency due to natural selection
may lead to the evolution of a new species.
Text Book: p. 54