Twenty-six strains of mice were tested for their reaction to four different sweet substances; saccharin, acesulfame, dulcin and sucrose. There was considerable strain variation in the degree to which they found the sweet substances preferable to water. The variation in preference for any one sweet substance is very highly correlated with the variation in preference for the other sweet substances. This is interpreted to mean that there is only one sweetness receptor, although an alternative explanation in terms of variation in psychological motivation is not discounted. The difference between C57BL/6Ty and DBA/2Ty is largely due to a single gene, Sac.
SummaryPrevious work which appeared to show that some strains of mice taste glycine solutions as bitter has been found to be in error. The bitterness came from copper glycinate which formed in the brass drinking spouts. Taste testing with copper glycinate shows that the genetical data identifying the gene Glb are still valid. The close linkage of Glb and Rua has been confirmed. Most strains of mice prefer glycine solution to water, presumably because the glycine tastes sweet. The degree of preference for glycine is correlated with the degree of preference for other sweet substances such as saccharin or acesulfame. The gene dpa appears not to be involved.The sweetness tasting gene Sac has been mapped to chromosome 4 at 8·1 ± 3·4 cM distal to Nppa (formerly Pnd). The bitterness tasting gene Soa is very closely linked to Prp on chromosome 6 (no recombinants among 67 backcross progeny). It is suggested that the sweetness and bitterness tasting genes have descended from a common ancestral tasting gene which existed before the tetraploidization of the genome which took place in early vertebrate evolution.
Glycine tastes both bitter and sweet to mice but there are differences between strains in their ability to detect each taste. With respect to the bitter taste, fifteen strains were classified as tasters and twelve strains as non-tasters. The difference is due to a single gene, Gib (glycine bitterness). Cycloheximide tastes bitter to all mice at a concentration of 8 /IM, but strain differences in sensitivity to the taste of cycloheximide can be detected at lower concentrations. The BXD RI strains can be classified into two groups with respect to sensitivity to cycloheximide. This is probably due to the segregation of two alleles of a single gene, Cyx. A comparison of the distribution in RI strains of alleles of four bitterness-tasting genes shows that the loci are all closely linked and are probably in the order Cyx-Qui-Rua-Glb.
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