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Summary Isolation and Speciation A level Biology
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Year 1 Biology AQA A level notes. Achieved an A* in my final exam using these notes. They are based on the mark scheme requirements.
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Isolation and speciation summary notes14 March 2023 12:55
Allelic frequencies and how selection affects them
- Alleles of any individual organism may be combined with the alleles of any other
- Allelic frequency- the number of times an allele occurs within the gene pool
- Allelic frequency is affected by selection
- Selection due to environmental factors - selective pressures
- Those that have a selective advantage outcompete others (ie for food, shelter, mate
survive and reproduce - pass on advantageous allele- frequency increases
- Environmental changes affect the probability of an allele being passed on in a populati
and therefore the number of times it occurs within a gene pool - the qualities needed
survive change too- different individuals become the fittest for that environment (best
adapted)
- This does not affect the probability of a mutant allele, but the frequency of a mutant a
that is already present
- Evolution by natural selection is a change in the allelic frequencies within a populatio
Speciation
- Speciation- evolution of new species from existing ones
- Species- group of individuals that share same genes but different alleles- can breed to
produce fertile offspring
- Members of a species are reproductively separated from other species (can only repro
with same species)
Formation of new species (from allopatric and sympatric speciation)
- Formed by reproductive separation followed by genetic change due to natural select
- Individuals can breed with individuals in other populations
- Population becomes separated from other
- undergoes different mutations- mutations in one group not shared with the other
- Become genetically different from other group- each of the populations experiences
different selection pressures because environment of each is slightly different
- Natural selection then leads to changes in allelic frequencies
- Different phenotypes of each combination of alleles are subject to selection pressures
populations are adapted to local environment- adaptive radiation- leads to changes in
frequencies (evolution) of each population leads to reproductive separation
- Reproductive separation- means that populations would not be able to interbreed
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