The behavior is in marked contrast to the fondness for sweets shown by most omnivores and herbivores and even some carnivores such, as dogs.
"There is a molecular explanation for the common observation that the cat lives in a different sensory world than the cat owner," Joseph Brand, associate director of the Monell Chemical Senses Center in Philadelphia, and colleagues wrote in the inaugural issue of the Public Library of Science's journal
Genetics.
To find the molecular answer, Brand and colleagues sequenced the regions of the domestic cat's DNA that code for T1R2 and T1R3, a pair of linked proteins needed to form the sweet receptors on the mammal's tongue.
The cat's genetic material was then compared with the sequence and structure of the same genes in dog, human, mouse, and rat, all species that display a normal sweet taste.
It emerged that cats do not produce the T1R2 protein because the gene that codes for it — called Tas1r2 — doesn't work.
Researchers call it an "unexpressed pseudogene," a sort of molecular fossil that has lost its ability to function since it wasn't important for a species' survival.
