effective population size

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effective population size The average number of individuals in a population that actually contribute genes to succeeding generations by breeding. This number is generally rather lower than the observed, censused, population size, being reduced by the following factors:
a. a higher proportion of one sex may mate;

b. some individuals will pass on more genes by having more offspring in a lifetime than others; and

c. any severe past reduction in population size may result in the random loss of particular genotypes.

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