And here we have the genetic addendum to my Thunder redesign post.
(restating for clarity that this post is assuming that Toothless is indeed the last Night Fury aka there are no other “secret populations” hiding somewhere)
So, can bicolor Furies persist in the dragon population for 1000+ years across however-many generations? Well, let’s take a look.
Given that the Night Lights display patches of both black and white scales, we can assume that Fury colors work somewhat similarly to those of domestic cats.
For those who don’t know, cats have two main color genes: black and orange (which can then be modified by other genes into a variety of other colors; for example, the dilution gene turns black into blue and orange into creme–but we don’t need to worry about that here).
The black and orange genes are equally dominant, so when both are present in a single individual, they create a sort of patchwork pattern of both colors on the coat, aka tortoiseshells (or calicos if the cat also happens to have the white spotting gene but again we don’t need to go into that here).
The same thing seems to be happening with the Night Lights, though unlike cats whose main color genes are located on the X chromosome and are therefore sex-linked (torties and calicos are almost exclusively female with the very rare exception of XXY males, who are usually sterile), dragon color genes appear to be on a different chromosome, so both males and females are equally able to inherit both.
Here’s a chart showing this “co-dominance” over a few generations of Toothless’s lineage interbreeding with Light Furies (yes I know Ruffrunner isn’t on there, but it was easier to organize the chart with just two; he has the same night/light distribution as his siblings anyways):
As you can see, any bicolor Night Light, no matter how far removed from Toothless himself, still has a 50% chance of passing on a black gene to their offspring, hence continuing bicolor patterning!
And that’s not all. Let’s say that after several generations there are two Night Lights. They both retain the black gene, but enough time has passed that they are not too closely related to each other, let’s say idk eighth cousins or something. Let’s say they become mates and…
WOW! We can get fully black Furies again! Cool!
But is this technically a Night Fury? Well…there’s more to a “Night Fury” than just black scales, so it’s gonna be a little more complicated than that.
Let’s go back to our first-generation Night Lights, the direct offspring of Toothless and Nubless. Because Toothless can only contribute Night Fury genes and Nubless can only contribute Light Fury genes, we know that all of the og Night Lights have one copy of each species’ gene in their genotype. We can then look at their phenotype (outward appearance) to determine which ones are dominant and which are recessive.
Taking this approach, it appears that Night Fury back spikes are dominant over the Light Fury back fin. So what does that mean for future Night Lights?
Any Night Light who possesses the Back Spikes gene will have at least a 50% chance of passing it to their offspring when breeding with a pure Light Fury. Once enough generations have passed for Night Lights to start interbreeding with each other, the chance for a pair of heterozygous (Sf) Night Lights to have back-spiked offspring will be 75%. Two Sf Night Lights will also have a 25% of producing a homozygous (SS) dragon, which in turn will pass the spikes to 100% of its offspring even when breeding with a pure Light Fury.
So Back Spikes will be less common than Back Fin despite being dominant, at least for the first several generations, simply because it’ll be a handful of Sf Night Lights breeding with an abundance of ff Light Furies; however, as long as the spiked individuals continue to breed the trait should be able to remain in the gene pool for a decent amount of time, and will eventually becoming more common as it becomes possible for Sf’s to interbreed with each other.
But now let’s look at the recessive traits. While our og Night Lights have spikes on their backs, they also have fins on their legs, so we can assume that Leg Spikes are recessive to Leg Fins. Let’s revisit our chart again.
Because our heterozygous Night Lights are breeding with dominant-homozygous Light Furies, the Leg Spikes trait will completely disappear from the phenotype for the next several generations…
….but not necessarily from the genotype. While none of the earlier Night Lights will display Leg Spikes, they can still carry the gene. I’ve marked these carriers in blue. Fs Night Lights would have a 50% chance of producing another Fs Night Light when breeding with FF Light Furies.
Which, in turn, brings us back to that time when Night Lights can start breeding with each other. FF+Fs cannot produce ss…but Fs+Fs can, albeit only with a 25% chance, and we could get our first phenotype Leg Spikes in ages!
So clearly all Night Fury traits have the ability to persist through the generations, be they a constant part of the population or something hidden that crops back up later. Does that mean we could eventually get another proper Night Fury?
Yes, it is possible to get a fully black Fury again even though it is codominant with white.
Yes, it is possible to keep Back Spikes and other dominant traits within the lineage for generations to come.
Yes, it is possible for Leg Spikes and other recessive traits to reappear eventually.
But how likely is it for all these traits to just so happen to coincide on the same dragon? Alas, probably not very. Possible, yes, but very very rare/unlikely.
So, here’s what I think the future of the Fury population would look like:
Pure Light Furies and White Night Lights would be the most common. Bicolor Night Lights are also moderately common, and Black Night Lights are rarer but not unheard of. Physical Night Fury traits are sprinkled throughout Night Lights of all colors–some have extra nubs, some have back spikes, some have leg spikes…many have none and a rare few have all.
And maybe, just maybe…one particularly lucky dragon just so happens to look a whole lot like a Night Fury.
threefeline