AQA A Level Biology

Revision Notes

7.3.6 Reproductive Separation

Reproductive Separation

Reproductive separation

  • In order for evolution to occur the new species population must be genetically and reproductively separated from the pre-existing species population
    • When this happens, there can no longer be an exchange of genes between the two populations
  • Reproductive separation occurs when changes in the alleles and phenotypes of some individuals in a population prevent them from successfully breeding with other individuals in the population that don’t have these changed alleles or phenotypes
  • Examples of allele or phenotype changes that can lead to reproductive separation include:
    • Seasonal changes – some individuals in a population may develop different mating or flowering seasons (becoming sexually active at different times of the year) to the rest of the population (i.e their reproductive timings no longer match up)
    • Mechanical changes – some individuals in a population may develop changes in their genitalia that prevent them from mating successfully with individuals of the opposite sex (i.e. their reproductive body parts no longer match up)
    • Behavioural changes – some individuals in a population may develop changes in their courtship behaviours, meaning they can no longer attract individuals of the opposite sex for mating (i.e. their methods of attracting a mate are no longer effective)

Genetic isolation

  • When two populations of the same species become reproductively isolated from each other, they can eventually become genetically isolated
    • If the two populations are no longer reproducing with each other, then they do not interchange genes with each other in the production of offspring
    • Changes that occur in the allele frequencies of each group are not shared, so they evolve independently of each other, which can lead to the formation of two populations that are no longer successfully able to interbreed
    • When the genetic differences lead to an inability of members of the populations to interbreed and produce fertile offspring, speciation has occurred

Reproductive separation, downloadable AS & A Level Biology revision notes

Reproductive separation of two populations can lead to speciation


Alistair graduated from Oxford University in 2014 with a degree in Biological Sciences. He has taught GCSE/IGCSE Biology, as well as Biology and Environmental Systems & Societies for the International Baccalaureate Diploma Programme. While teaching in Oxford, Alistair completed his MA Education as Head of Department for Environmental Systems and Societies.

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