Taste Thresholds in Twins and Siblings

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Abstract
Monozygotic twin (MZ), dizygotic twin (DZ), and sibling (SIB) pairs were taste-tested for hydrochloric acid, 1-quinine sulfate, and 6-n-propylthiouracil (PROP). The numbers of pairs involved were 75 MZ, 70 DZ, and 78 SIB, for the latter two compounds; 26, 45, and 45, respectively, for the acid. There was a significant difference in intrapair variance, between the MZ and the same-sex DZ pairs, in thresholds for bitter-tasting 6-n-propylthiouracil (p < .001). The difference in intrapair threshold variance was not significant for bitter-tasting quinine (p > .05) or for sour-tasting hydrochloric acid (p > .10). The male MZ pairs had a significantly lower intrapair threshold variance than the male DZ or male SIB pairs for hydrochloric acid (p < .01), but the female pairs manifested no such difference. The intrapair variance in hydrochloric acid threshold was significantly less for the nine male MZ pairs than for the 17 female MZ pairs (p < .02). Repeated taste tests on the same subjects reproduced results similar within a single threshold range in a high proportion for each compound: for hydrochloric acid, 72.9% (N = 44); for quinine, 76.9% (N = 221); and for PROP, 76% (N = 225). Correlations between thresholds for the different substances were positive and significant (N = 308): between PROP and quinine, r = + 0.44 ± .05 (p < .01); between quinine and hydrochloric acid, r = + 0.35 ± .05 (p < .01); between PROP and hydrochloric acid, r = + 0.17 ± .06 (p < .05).