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Geographical Isolation

Specification: Geographic separation of populations of a species can result in the accumulation of difference in the gene pools. The importance of geographic isolation in the formation of new species  

Exam question on geographical isolation: Changes in ecosystems can lead to speciation. In Southern California 10 000 years ago a number of interconnecting lakes contained a single species of pupfish. Increasing temperatures caused evaporation and the formation of separate, smaller lakes and streams. This led to the formation of a number of different species of pupfish.Explain how these different species evolved. (5 marks)
Mark scheme: 
1. Geographical isolation
2. Separate gene pools/ no interbreeding (between populations) due to the separation of the lakes
3. Variation due to mutation 
4. Different envionmental/abiotic/biotic conditions/selection pressures
5. Selection for different/advantageous, features/characteristics/mutation/alleles
6. Differential reproductive success/ (selected) organisms survive and reproduce
7. Leads to change in allele frequency
8. Occurs over a long period of time

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