| Traditionally the issue of heterosis has been posed in genetic terms such as dominance and overdominance. |
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| With overdominance, unlike alleles are postulated to result in a stimulating effect, so that genetic heterozygosity per se produces heterosis. |
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| The fixation of deleterious mutations may be a general explanation for heterosis in crosses between ecotypes, despite alternative overdominance interpretations. |
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| One of many well-investigated examples of overdominance in animals is the colour polymorphism that exists in the marine copepod crustacean Tisbe reticulata. |
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| This situation, known as heterosis or overdominance, leads to the stable coexistence of both alleles in the population and hence contributes to the widespread genetic variation found in populations of most organisms. |
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