The apple's mythological career is large, and one of its most famous appearances is a mistranslation.
Genesis does not name the fruit of the tree of knowledge. The Hebrew says only fruit. The apple entered through Latin: malum means apple, and malus means evil, and the pun was available to Latin-speaking commentators and artists from late antiquity onward. By the medieval period the apple was fixed in Western art, and Milton uses it. Eastern Christian and Jewish traditions variously suggest fig, grape, pomegranate or wheat. The apple is a Western European accident of vocabulary.
The genuine apple myths are elsewhere and are consistently about immortality or discord. The golden apples of the Hesperides, guarded at the world's western edge, are Hera's wedding gift and the object of Heracles's eleventh labour. The apple of discord thrown by Eris, inscribed to the fairest, sets off the Judgement of Paris and the Trojan War. In Norse tradition Idunn keeps the apples that hold the gods' youth, and their loss ages them immediately. In Irish and Welsh material the otherworld is repeatedly an island of apple trees; Avalon, Insula Avallonis, is generally understood as the place of apples, from a Brittonic word cognate with Welsh afal.
The domestic apple's actual origin is genuinely remarkable and was only established by genetic work in recent decades: it descends principally from Malus sieversii, a wild apple of the Tian Shan mountains in Kazakhstan, and moved west along the Silk Road. Apples do not come true from seed, so every named variety is a graft, and orchards are clonal.