EDIT: According to MLP:FiM episode BABY CAKES, this chart and its sequel chart (mixed blood pairs -- generation skips) are COMPLETELY SHOW ACCURATE except possibly for alicorns (no proof at current time, but it still seems likely that alicorns can bear with anypony from the main three types at least)
EDIT: Added possibility of triplets produced from alicorn pairs. I am fully aware that fertilized eggs don't split in thirds for triplets, I just don't have a better way to describe it at the moment and after doing two full charts of these and explaining everything in detail, I'm tired. If you know the correct phraseology for triplet eggs, cool beans, I'll change the chart if you can tell me. Just don't be a jerk in the comment section, okay? It's a freakin' children's television show. Real World limitations don't apply and hey, pobody's nerfect. The fandom is about love and tolerance, so verbal attacks on my intelligence are immature and against everything the show teaches in the first place. I did the best I could to explain it; if that's not enough for you, then do something better and show me up. Idc. I'm cool with that as long as you're having fun.
UPDATE: Included Faust confirming the ponies themselves can in fact crossbreed, for those of you insisting that they cannot. Also included some extra info for each subheading. Lastly created another chart for mixed blood ponies, which you can see here: [link]
for all you Derpy x Dr. Whooves people who believe Sparkler and Ditzy Doo are their children. This second chart proves it's possible if Derpy has a unicorn in her ancestry!
---------This chart can help you create family trees for your pony pairings--trace how traits transfer from your pairings to their children and show you what children can be produced from what kinds of pairings.
Male ponies are in BLUE
Female ponies are in PINK
Foals are in PURPLE, and are genderless (as they can be either gender)
Unicorns have RARITY HAIR and a HORN
Pegasi have RAINBOW DASH HAIR and WINGS
Earth ponies have APPLEJACK HAIR and a HAT
so that you can tell them apart
A chart of what kind of foal will be produced depending on the genetic traits of both parents.This chart assumes that the pony parents are pure blooded unicorns, pegasi, earth ponies, and alicorns
If a foal is a unicorn when one parent is a pegasus and the other parent is an earth pony, then that means that one of its ancestors MUST have been a unicorn, and that the genetic trait skipped the parents' generation and became apparent in the foal's generation. Therefore, for an example, you can still produce a pegasus from two earth ponies--but only if there was a pegasus further back in its ancestry, otherwise this would be impossibru.
Genetic Chart Explained:
Unicorn + Unicorn = Unicorn
Pegasus + Pegasus = Pegasus
EarthPony + Earthpony = Earthpony
Unicorn + Pegasus = 50% Chance of Unicorn foal, 50% Chance of Pegasus foal
Pegasus + Earthpony = 50% Chance of Pegasus foal, 50% chance of Earthpony foal
Earthpony + Unicorn = 50% Chance of Earthpony foal, 50% Chance of Unicorn foal
Unicorn + Earthpony = 50% Chance of Unicorn foal, 50% Chance of Earthpony foal
Pegasus + Unicorn = 50% Chance of Pegasus foal, 50% Chance of Unicorn foal
Earthpony + Pegasus = 50% Chance of Earthpony foal, 50% Chance of Pegasus foal
(Winged Unicorns) This is where it gets a little tricky.
Alicorns are a combination of all three pony types-- UNICORN, PEGASUS, and EARTHPONY all at once. Now according to pureblood genetics, the original three above (earthXearth, pegasusXpegasus, unicornXunicorn) this means that an alicorn could theoretically mate with any pony type and produce a foal. However, the alicorn would act as the second unicorn when mating with a unicorn, the second pegasus when mating with a pegasus, or the second earth pony when mating with an earth pony, because it possesses all three types of pony magic. The other two types of pony magic would lie dormant, but not be all visible at once in the foal.
Alicorn x Unicorn = Unicorn
Alicorn x Pegasus = Pegasus
Alicorn x Earthpony = Earthpony
Because basically in each pairing, the single-type pony's genes would match with the same genes of that type which the alicorn possesses, and the other two magic traits the alicorn possessed would lie dormant instead.
With Alicorn x any other pony type, the type of pony the second pony is would determine the nature of the foal because it would present a 100% match gene-for-gene, while the other two pony traits would lie dormant as they would only be an unmatched 50%.
Alicorn x Alicorn = Alicorn
^ This is the only situation in which another alicorn could be produced from a pairing, because both alicorns would be matching each other trait for trait.
In other words, SINGLETRAIT + SINGLETRAIT = SINGLETRAIT, whereas SINGLETRAIT + DIFFERINGTRAIT = 50/50 CHANCE OF TRAITS.
In an alicorn x alicorn pairing, it would basically be unicornXunicorn, pegasusXpegasus, and earthponyXearthpony all at once, and each trait would then be present in the foal.
We can safely assume that Alicorns can indeed
mate with all ponies because of Prince Blueblood's relation to the alicorns by word of Goddess (A.K.A. Lauren Faust) who said he is the "great great great great great great great great great great great (and probably even more greats) nephew on Celestia's and Luna's mother's side, about 52 times removed, roughly speaking." Since he is a unicorn and not an alicorn, meaning he must have unicorn blood in him along with alicorn blood. Since the name "BlueBlood" literally means to have Royal Blood, it is also safe to assume he is directly related to the alicorns and not adopted into the family as some may claim. Particularly including the fact that this is a children's show, it is difficult to believe that he was adopted into the royal line or that an ancestor of his was adopted into the royal line, as this would certainly have been explicitly mentioned somewhere in the show as it would be a plot device for sure. However the possibility of adoption was not ever stated or even implied, and along with his name literally meaning Royal Blood, we can assume he is in fact a descendent of alicorns who does not carry wings or lay claim to earth pony magic. ZEBRAS
I considered adding zebras to the chart because of Zecora. However, because we do not see any striped pegasi or striped unicorns, or even any Zebra x Earth pony pairings, it is difficult to say at this time whether Zebras can even mate with ponies or alicorns at all. I am not going to hazard any guesses at this point. I think what I have in the chart is logical and feasible however. DRAGONOSKIS
Because dragonoskis are just so different from earth ponies, unicorns, pegasi, and alicorns in every way, I'm going to say that it's highly unlikely that a dragonoskis could ever mate with any pony type and reproduce successfully.
This does not mean that Discord could not mate with any pony type, it only means that he and his partner-of-your-choice could in all likelihood never reproduce, simply because they are too far removed in terms of animals. You don't see mice mating with eagles, because they cannot bear children together, and so I think it would be with a dragonoskis and a pony.