A trait that always appears in two opposite forms is called a __________ trait.

In genetics, a contrasting trait refers to a characteristic that manifests in two distinct, opposite forms such as tall vs short, or round vs wrinkled seeds. Mendel's work on pea plants focused specifically on such contrasting traits because they were easily observable and followed predictable inheritance patterns. Recessive and dominant describe how traits are inherited, not their appearance in opposite forms. Polygenic traits involve multiple genes and don't appear as simple opposites.