A level Biology B · Edexcel 9BI0 · Topic 8D
Speciation
Key points
- Speciation is the formation of new species when populations become reproductively isolated, so gene flow stops.
- Allopatric speciation: a geographical barrier separates populations; different mutations and selection pressures change allele frequencies until they can no longer interbreed.
- Sympatric speciation: occurs in the same area, e.g. by polyploidy in plants or by different feeding or breeding habits.
- Isolating mechanisms: behavioural (courtship), seasonal/temporal (breeding times), mechanical (genitalia or flower shape), gametic, and hybrid inviability or sterility.
- New species are confirmed by failure to produce fertile offspring and by differences in DNA sequences.
- Molecular evidence (DNA, proteins) helps build phylogenetic trees showing common ancestry.
Topic notesPremium
A species is a group of organisms that can interbreed to produce fertile offspring. New species form when populations stop exchanging genes and evolve apart until they can no longer interbreed successfully.
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