Definition: a quantitative genetic trait with a continuous distribution termed its liability; may generate two kinds of phenotype, according to whether the liability lies above or below some critical threshold at about which a radical change in behavior occurs. For instance, blood uric acid level is a liability with an approximately gaussian distribution. At a critical point of chemical saturation (the threshold), crystallization occurs and the resulting gout or nongout is a threshold trait.
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Examples: glitazone, GI cocktail, etc.