5.5 Population Genetics- Isolation & Speciation

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  • Created by: Rebecca
  • Created on: 21-06-11 12:28


  • Within a population of one species there are groups of interbreeding individuals.
  • Within each populations there are breeding sub-units called demes.
  • Individuals in a deme tend to breed with each other more often than they do with individuals of other demes. 
  • New species arise when some barrier to reproduction occurs so that the gene pool is divided and the flow of genes between separate demes may cease.
  • Such a barrier which effectively prevents gene exchange between demes is called an isolating mechanism.
  • If the separation is long-term, eventally the two groups will be so different that two new species, incapable of interbreeding, are formed.
  • The separate species will each have their own gene pool. This process is called speciation.

Isolation Leading to Speciation:

  • For new species to develop from a population, some form of isolating mechanism is required.
  • There are two main forms of isolating mechanisms.

Forms of Isolating Mechanism:

  • Geographical isolation. This occurs when the population become physically split into separate demes. The physical barrier may be a mountain or a river or any feature which prevents the population of the


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