Eye color, hair color, skin color, height, and blood type are examples of phenotypical features that present two or more varieties. Other examples are the color of flowers and seeds in some plants, the sex of the individual in dioecious species, etc. Examples of phenotypical characteristics that do not present variation among individuals of the same species are: in general the number of limbs, the anatomical position of the organs, the general composition of tissues and cells, etc.
The possibility of a phenotype presenting natural variations (in organisms of the same species) is necessarily determined by two or more different alleles of the corresponding gene. These different alleles combine and form different genotypes that condition the different phenotypes (variations).