allelomorph

From allelo- (“other”) +‎ -morph (“shape”), from Ancient Greek ἀλλήλων (allḗlōn, “one another, each other, mutually, reciprocally”) from ἄλλος (állos, “other”). Coined by English biologists William Bateson and Edith Rebecca Saunders in 1902, in a paper titled "The facts of heredity in the light of Mendel’s discovery".