Yeah, orcs can't breed with elves in ADnD. Kind of odd since (in Tolkien anyway) they were genetically engineered from elves so should still retain basic genetic compatibility (not that fantasy realms have anything to do with science though :P.) They can breed with just about anything else though.
Orcs will crossbreed with virtually every humanoid and demihuman species except elves, with whom they cannot. The mongrel offspring of orcs and these other species are known as half-orcs. Orc-goblins, orc-hobgoblins, and orc-humans are the most common. Half-orcs tend to favor the orcish strain heavily, and as such are basically orcs, although 10% of these offspring can pass as ugly humans... Elite orcs, or orogs, are a race of great orcs, possibly mixed with ogre blood.
Elder Scrolls has something similar to the 'orcs from elves' theme, but their orcs used to be elves until their god was similarly transmuted into a demon like being. Though I think Elders Scrolls are a bit nuts with the 'elves galore'. Even their dwarves are elves (even if they are all missing).
@RedGuard - elves are abysmally ugly in ES though (at least Skyrim) - orcs are almost fetching by comparison. So in that world, I'd be willing to believe elves were the genetic mutants derived from orcs .
Also, everyone knows DnD got its orcs from Tolkien regardless of whether they tried to obscure that later on (and hobbits or "halflings" for that matter). Elves, dwarves and such were common fantasy races going back to the earliest Norse epics but orcs and hobbits were Tolkien's own creations (based partly perhaps on other mythical creatures but they were still his inventions).
Indeed they are based on them... but they are still very different beast, like i said in D&D multi verse they arent twisted elves... they are the progeny of the god Gruumsh in at least 75% of the D&D verses
Comments
Also, everyone knows DnD got its orcs from Tolkien regardless of whether they tried to obscure that later on (and hobbits or "halflings" for that matter). Elves, dwarves and such were common fantasy races going back to the earliest Norse epics but orcs and hobbits were Tolkien's own creations (based partly perhaps on other mythical creatures but they were still his inventions).