Which of the following describes a variation that has no intermediate forms?

Discontinuous variation is characterized by distinct categories or phenotypes with no intermediate forms between them. This form of variation typically arises from the influence of one or a few genes and can result in traits like blood type (A, B, AB, O) or the presence/absence of particular physical characteristics (for example, the ability to roll one's tongue versus not being able to).

In contrast, continuous variation involves traits that do show a range of intermediate forms, such as height or skin color, which are influenced by multiple genes and environmental factors. Genetic variation refers to the diversity in gene frequencies within a population, and environmental variation pertains to differences in traits that arise due to environmental influences rather than genetic assembly. Discontinuous variation specifically highlights how certain traits can be categorized without any in-between states, thus making it the correct choice in this context.