Genetics Picture

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Sometimes the phenotype for the heterozygotic individual is more extreme than both the homozygotic varieties. That is, if pp gives a light pink flower and PP gives a dark pink flower, then Pp gives a dark red flower! And that feels a little unexpected. This phenomenon is called over-dominance and occurs among other things in the immune system: individuals that are heterozygotes for genes of the immune system, are often healthier and have a better chance of survival than individuals that are homozygotic (with whatever allele) for these genes.