Genetic saturation is the reduced appearance, which occurs over time, of sequence divergence rate that results from reverse mutations, homoplasies and other multiple changes occurring at single sites along two lineages.
Genetic saturation occurs most rapidly on fast evolving sequences, such as the hypervariable region of mitochondrial DNA, or in Short tandem repeat such as on the Y-chromosome.
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Saturation (genetic) Wikipedia(Text) CC BY-SA