The ability to taste PTC (phenylthiocarbamide) is not an example of morphological variation, but rather a physiological variation, as it relates to taste perception, which is a functional trait, not a structural one. 

• Morphological variation: refers to differences in the physical structure or form of an organism, such as variations in bone structure, skin color, or body shape. 
• Physiological variation, on the other hand, relates to differences in the function or processes of an organism, such as variations in metabolism, hormone levels, or, in this case, taste perception. 
• The ability to taste PTC is determined by a single gene (TAS2R38) that codes for a bitter-taste receptor on the tongue. 
• Different variations, or alleles, of this gene determine whether PTC tastes bitter or not. 
• The ability to taste PTC is a classic example of a genetic trait that varies in human populations, and the variation is linked to the function of a specific taste receptor.