It’s pretty cool, looking at this from a genetics standpoint… It shows that Rainbow’s manestle is a recessive trait - assuming manestyle is something determined by genes and not… Y’know, what you want your hair to look like - while her mane color is a dominant trait. Likewise, Pinkie’s manestyle is dominant, and her mane color is recessive. Rarity’s mane color and manestyle are both dominant traits. As far as eye color goes, Dash’s magenta seems to be recessive, while Rarity’s dark blue is dominant, and Pinkie’s sky blue is recessive. For coat colors, Dash’s is definitely recessive, while Rares’ coat color is also recessive, and Pinkie’s pink is dominant. Honestly, the only dominant gene Dash has, really, is her Cutie Mark - again, assuming that’s a genetic trait. Every Cutie Mark fusion except Raripie has Dash’s trademark lightning bolt, and all Cutie Marks involving hers are in the same general pattern; large shape, with a lightning bolt coming from said shape.
…Of course, with RariDashiPie, all bets are off cause it’s a mixture of six different genes for everything.

Raridash is best pony.