The Founder Effect

The Founder Effect: Occurs when a small number of individuals from a population found a new population that is reproductively isolated from the original one. It is a special case of Genetic Drift and can be seen in the Amish populations of the United States - they have grown from a very few founders, have not recruited newcomers and tend to marry within the community.

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Example: Spotted=ss, Non-Spotted=SS or Ss

The New Population Is Made Up Of Spotted Giraffes, All With The Recessive Allele,
 Making Them Unable To Have Non-Spotted Offspring

A Smaller Gene Pool And Allele Frequency Is The Result

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The effect of Genetic Drift is inversely related to population size:

Large Population = Small Effect - Little change in allele frequency.

Small Population = Large Effect - Dramatic change in allele frequency.