A friend of mine who started playing fairly recently has decided she doesn't want to deal with the complexity of genetics in this game. I tried to explain how (I thought) it worked, but after looking at this problem child she hatched, I realized I don't understand it either.

She didn't want demon wings on her qitaris, and so bought tested parents who didn't have it. And she got it anyway. Both parents have that mutation in their background, I realized after I looked at their lineage, but I do not understand how this offspring got it if neither parents shows it visible OR carried?

If genetic testing doesn't show all the genes, what is the point? And how does this work?

Can someone explain this horse?

https://www.sylestia.com/view/pets/?petid=4090511

The mother has Demon Wings as a Hidden trait (aka, a carried under her pegasus wings):
Mutation Three: (AB) Pegasus Wings

Looking at the lineage, it's:
4090511/Un-Named has (BD) Demon Wings (but is untested, so shows (BB) Demon Wings in his genetics- you cannot see either Carried or Hidden traits in the genetics section of untested pets, just like you can't tell exact genes in real life unless they're the phenotype (expressed traits))
He got the D (butterfly wings) from his father, who is (ND) Butterfly Wings, but could alternately have gotten the N (no vis).

His vis B (demon wings) is from his mother, from whom he could have alternately gotten A (Pegasus Wings).

His mother, Wing, got her pagasus wings vis from her maternal grandfather, Flares- his daughter, her mother, Firework Flash, being M3: (NA) Pegasus Wings.
She got her Hidden Demon Wings trait from her paternal grandmother, Light; Wing's father, Fasloe, is M3: (AB) Pegasus Wings, and passed on his B (demon wings) not his A (pegasus wings)

The possible genetic outcomes from this pet's parents (Rainbow Mane and Wings) in the M3 are:
NA (Carried Pegasus Wings)
NB (Carried Demon Wings)
AD (Vis Pegasus Wings, hidden Butterfly Wings)
BD (Vis Demon Wings, hidden Butterfly Wings)

https://www.sylestia.com/forums/?thread=37255
That there is the Link to Taps extension thread, It works really well for Visual people like me and allows you to see on a tested pet what traits are hidden and what not. might be of some help ^^

it also gives you buttons for wardrobe an a bunch of other useful features