In the world of Shadowrun, can metahumans (i.e. non-humans, such as elves or dwarves) interbreed with each other or with humans? For instance, can a half-elf, half-human exist? Or a half-ork, half-troll? Or is it only possible for metahumans to have children with their own metatypes?
I suspect that the novels or video games may have information about this. Site policy is that you can answer from them if you want to, just be careful about any differences they may have from the RPG.
Yes, they can interbreed.
No, you don't get "mixed breeds"
Contrary to ethnic races, metagenes seem immune to recombination, miscegenation, and dilution. Although members of different metatypes are able breed with one another, the child always expresses only one of the parent’s metatypes—or is born human (as a result of conflicting metagenes suppressing expression).
(SR4 Runners Companion, 46)
So, a child born to parents of different Metatypes will either come out as Mom's Metatype, Dad's Metatype, or as an ordinary Human.
Perhaps also of note, is that this applies to Metavariants* as well:
Medical studies on the procreation of metavariants have also indicated that children of different metavariants of the same metatype either express the paternal or the maternal metavariant-type. Crossbreeds between different metavariants or baseline metatypes and metavariants appear to be impossible, though the reason for this exclusivity is currently unknown.
(SR4 Runners Companion, 48-49)
* Metavariants are sub-types within a Metatype, generally a lot rarer than the base Metatype and focused around a geographic location. For example, under "Dwarf" you can find: Gnome (Europe), Harumen (India), Koborokuru (Japan), Menehune (Hawai'i), and Querx (Germany). They are considered derived from their parent Metatype, but are different enough to count as 'unique.' In 5E, you can find details on them in Run Faster, starting at page 88.
Regarding more recent editions (5th and 6th), there is no information written in any of the sourcebooks that would contradict, overwrite, or update this lore from 4th Edition. Since we have no new information regarding metatype reproduction, this is the most 'up to date' answer available.
While mechanics change from edition to edition, lore is often assumed to persist in Shadowrun (newer editions freely reference events, characters, etc. without actually explaining them). Thus, with no contradicting evidence, it is likely that the 4E standards on metatype interbreeding remains the official lore.
Genes in Shadowrun are weird, as of at least 4th edition.
An "Ork" isn't "the product of two Ork parents." It's "a metahuman whose genes manifest closer to an Ork metatype than another other metatype." Elves, Humans, Trolls: they are all the same species, just with different gene markers. I guess that's what happens when genetics meets magic.
Races in Shadowrun are similar to eye color in real-life. If you look at the parents, you can usually figure out what the kid's eyes are going to look like, but not always, and never with 100% certainty. Not only can metahumans typically breed with one another, but their child could easily be the type of either parent, a human, or (much less likely but still possible) a completely different metahuman type altogether.
So someone with an Ork parent and a Troll parent is probably just an Ork or just a Troll, but there's a slim chance they could be something else.
Any metatype can breed with any other, in fertility terms anyway. Because of the way metagenes work you can't get true half-breeds but Changelings can look like half-breeds, and apparently even full metatype individuals may not look particularly like the metatype they technically belong in given the existence of the Human-looking trait and it's effects.
