Negative and positive selective pressures shape genetic variance through frequency-dependent selection.
Negative selective pressure is when a trait is disadvantageous and reduces an individual's fitness, leading to a decrease in genetic alleles that lower species' fitness. On the other hand, positive selective pressure occurs when a trait is advantageous and increases fitness, resulting in the prevalence of successful alleles in the population.
Additionally, negative frequency-dependent selection selects for rare phenotypes, increasing genetic variance, while positive frequency-dependent selection chooses common phenotypes, usually decreasing genetic variance.
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