Seventy-four pairs of monozygotic(identical)twins and 35 pairs of dizygotic(fraternal)twins provided recognition thresholds(modified Harris-Kalmus test)for the sourness of citric acid and the saltiness of sodium chloride during the Twins Days Festival in Twinsburg,OH.Variance components(ACE)models were applied to the data:total variation = additive genetic(A)+ common environment(C)+ nonshared environment(E).The best-fit model of variation in recognition thresholds for sourness included an additive genetic factor,accounting for 53% of the variance,but no common environment component.This level of heritability,on par with that of sensitivity to the bitter compounds 6-n-propylthiouracil and phenylthiocarbamide,strongly suggests that genetic factors play a larger role than shared environment in determining individual differences in recognition thresholds for sourness.In contrast,the best-fit model for saltiness recognition included a common environment component,accounting for 22% of the variance in thresholds,but no additive component.This result suggests that environment plays a larger role than genetics in determining individual differences in recognition thresholds for saltiness.
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