I've read from a book somewhere that when you selectively breed foxes to become loyal and dog-like, they start evolving color patches and curled ears just like dogs', implying these genes are all connected.

I actually know about this! Yeah, this experiment (conducted in Novosibirsk, Siberia, since about 1952) on silver foxes-- a dark color mutation of the red fox-- was, and apparently still is, a real thing. Though I'd define its purpose somewhat differently: testing whether selectively breeding for tameness (or more properly neoteny, of which tameness is an outgrowth) could also cause changes in a species's morphology (physical structure), as was posited had been the case with domestic dogs.

For those of us who are interested in genetics, animals, and especially neoteny (which has profound implications for humans), this is all very cool... but what the hell has it got to do with trans bullshit??? Yeah, the experiment confirmed that the presence of a more neotenous brain (i.e., one that retains juvenile characteristics-- such as docility ["tameness"], but also plasticity, the source of learning ability, and thus human intelligence-- in adulthood) causes more neotenous physical traits to manifest... and so... uh... trans people have more neotenous brains and look younger than their age... or something...? Yeah, I have no idea. And I doubt that this dude-with-ladyfeelz Redditor does either.

Link for the experiment, in case anyone's sufficiently intrigued: https://en.wikipedia.org/wiki/Domesticated_silver_fox