I like genetics and couldn’t resist playing with how a realistic-ish approach to colors and body features might work.
Fluffy types:
The original fluffy pony bio-toy concept had an emphasis on breeding. Plain-looking ‘earthies’ would be sold that would then have diverse litters- a fun surprise for kids that was possible through these traits being controlled by multiple genes. A total of six genes was used to accomplish this.
First there was the ‘growth’ locus with three possible alleles- the dominant Ng which inhibited all growths, the recessive grh which allowed for horn growth and grw which allowed for wing growth. A unicorn must have grhgrh, a pegasus must have grwgrw, and an alicorn must have grhgrw.
All Breeding Surprise! earthies were sold with either Ngrh or Ngrw. There was no visible distinction between the two.
However, this alone was not enough. This would be too easy for casual breeders to figure out, so there were also ‘horn’ and ‘wing’ loci that controlled the development and type of horns and wings.
The horn locus had the dominant ‘no horn’ Nh allele- even if a fluffy was grhgrh it would lack a horn if Nh was present. There was also the simple horn (h), a glowing horn (gl), a two-tone horn (tt), and a sparkling horn (sp). Glow was recessive to both two-tone and sparkle, while two-tone and sparkle were codominant with each other.
The wing locus similarly had a dominant ‘no wing’ Nw allele, but only had two variations- large (wl) or regular (w), with large being recessive to regular.
This combined makes breeding alicorns from earthies an interesting challenge. Alicorns bred to alicorns do breed true, but have very reduced litter size and increased foal mortality.
Colors- The Base Coat
The rainbow of colors of fluffies is due to structural color rather than pigment. Under that structure is the standard eumelanin (black) and pheomelanin (red-brown) pigments found in mammals.
The distribution, dilution, and pattern of these are controlled rather simply- like a streamlined version of horse color genetics only capable of producing white, black, chestnut, flaxen, bay, cream, and dun.
More casual breeders often neglect these genes since they can be more difficult to see, but they do impact color. A black-based fluffy will look richer, whites more pastel, and rich browns adding a red cast to the overall color. These can be selected for to maximize the impact of designer colors.
Colors- Structural Color
Structural color of the body and mane is controlled separately by eleven genes each- five that additively control the concentration of cyan (c), magenta (m), and yellow (y), and three that impact saturation, and three that impact how bright or dark they are.
The cmy genes are all codominant with each other and the chart of structural color can be simply visualized with a triangular plot:
The more ‘mixed’ a color is, the harder it is to breed true as different combinations of alleles can produce the same phenotype, so long as the ratio of c:m:y is the same.
Saturation impacts how strongly the structural color covers the base pigment. Like the hue, these genes have an additive effect. Even at the strongest saturation the base pigmentation still impacts the presentation of the color. Brightness and darkness are similarly straightforward.
Color- Patterns
Some patterning is impacted by base pigment- the mane of a monochrome bay will be noticeably darker than the body- but the more interesting patterns have different genes and mutations involved.
The mane being the same structural color as the body (monochrome) or different (bichrome) is a single gene. Bichrome (B) is dominant, monochrome (m) is recessive.
Pointed patterns are a different gene. No points (P) is dominant, while light points (pl) and dark points (pd) are both recessive and will cancel each other out.
Blotches are controlled by two genes like horn and wing growth- a potential gene and an expression gene. The potential has a dominant ‘solid’ (S) allele and a recessive ‘blotch’ (s) allele. After that the expression gene has another dominant ‘blank’ allele (B) as well as alleles for light (bl), dark (bd), no-cyan (bc), no-magenta (bm), and no-yellow (by) blotches. All blotch types are codominant.
The patterning of the blotches appears to have an inheritable component, but which genes and how they function are unknown.
White piebald spotting has a number of variations and new varieties frequently pop up as organic mutations in ferals.
Welp, anyway, that’s what I like to think about how genetics work here. I tried to accommodate for how certain things might be more or less common or valuable as well as building in some fun variety. Maybe you’ll find it useful, maybe you won’t, maybe I’m just a gay ass nerd. Idc.