Colour Genetics

I’m still learning and evolving, so please be kind if I haven’t got everything just right. I welcome any comments/opinions as long as they’re KIND 😊

So this is still a whole new world for me. I’ve been reading up on this since I chose Henley the day he was born, and he is now just over 2 years old. That’s a decent chunk of time and research, and I feel like I’ve only just begun to understand the tip of the iceberg. It’s pretty overwhelming and complex. We also did a little on Mendelian Inheritance patterns last semester at uni, and that definitely helped.

It’s hard to know where to start, so I’ll go back to basics.

"Phenotype" refers to what is physically displayed. "Genotype" refers to what genes the cat actually possesses. There are a lot of permutations as to what is displayed vs what is carried.

I’ve worked up some Punnett Squares to calculate the genetic, simple colour profile, and advanced colour profile of each mating. It looks confusing, but basically... it shows the colour possibilities of the offspring that [Henley x Nico] and [Henley x Adelaide] may produce. You can convert it to a percentage, but I think seeing it visually represented is easier.

Actually, all three, Henley, Nico and Adelaide, are genetically very similar. However, they each display a different phenotype.

They all have the black-based eumelanin colour. They all carry dilute. Henley and Nico are both tabbies (different patterns) but they both also carry the solid/non-agouti gene. I’ll get into all of that!

Henley is a black silver ticked tabby. I think he rates in around the medium-high silver range.

Nico is a black silver classic tabby.  I would class her as lower colour silver than both Henley and Adelaide. She also has more of a 'tarnished' or yellowed colour, compared to both Adi and Henley's white platinum-looking silver/smoke.

Adelaide is a solid black smoke. This means that she is non-agouti (no tabby pattern). I’d class her as a medium smoke level (I think ). Approx 1/2 of each hair shaft has smoking from the base.

For a little bit of context: The cats who have really high smoke/silver, all the way up to 'shaded' or ‘tipped’ levels... that's when over 4/5ths of the hair shaft are smoked/silver, and only the very tip of the hair has the base colour: black or red. Those ones can look almost entirely silver/white. They are very popular these days, and whilst they’re very striking, I’m not currently gunning for that. Henley actually does have at least one shaded cat in his lines, so I'd be really happy with some high smoke/silvers at any point! 

The nose leather and paw pads still correspond to the base colour, no matter how much silver or smoke you have. So if you have a black/blue base colour, the nose/pads will be black/dark. If you have a red/cream base colour, they will be pink/light.

This is interesting with Henley, he was born with black nose leather, but as he grew, he lost some of that pigment. It still has a black outline, but pink in the centre. All his paw pads are black. I think there's a name for the nose leather changing colour, but it's escaped me for now. 

So I think that's why everyone loves the the reeeeally high shaded or tipped cats who look almost all white with the the black base nose leather and black 'eye liner'. I must admit they are beautiful.

The silver is different to a solid white colour. The white gene actually works by masking over the base colour (I don't know heaps about white itself yet, that is another subject for another day).

Oh and to make it easier (or harder lol) the term "smoke" refers to a solid coat, and "silver" refers to a tabby patterned coat. It took me forever to figure that out.

Smoke/silver both come from the "inhibitor" (I/i) gene. It reduces or eliminates the production of pheomelanin or yellow pigment in the cat's hair. I believe it’s a dominant gene, which means you only need the one allele (I/i) to possess the phenotype.

The presence of two alleles (I/I) further reduces the "tarnished" colour, which can mean with those two alleles you'll get a stronger, brighter silver and less yellow than just with one copy of the allele.

If I was to guess, I'd say Henley and Adi are both homozygous I/I for the inhibitor gene, whilst Nico may be heterozygous I/i.  

I use the word 'guess', because I'm not sure there is a genetic test yet for the I gene in the normal DNA screens? I hope I’m wrong with that, because it's something I'd love to test for, but all of my current DNA tests haven’t included it. As it’s dominant though, if your cat has it, then it will likely pass it down.

I’m getting ahead here, so let’s go back to the black dominant base colour gene (B/b). It codes for eumelanin pigment. The dominant allele is ‘B’ which codes for black, and the recessive allele is ‘b’ which codes for brown.

The other base colour is the co-dominant red gene (O/o). This is sex-linked and found only on the X chromosome. It codes for phaeomelanin. The dominant allele ‘O’ codes for orange tones, and the recessive allele ‘o’ codes for non-orange pigmentation (so you default back to black or brown).

Males only carry one copy of the X chromosome, so that means they can only carry one of the alleles, either O or o. Not both. If they carry the dominant O, they will be red (or cream, if they also have dilute) OR they won’t – which means again, they default back to black or brown.

Females have two X chromosomes, so they’ll carry the two alleles. They can be homozygous O/O which codes for red, or heterozygous O/o which codes for tortoiseshell, or recessive homozygotes o/o which codes for the default black or brown.

That’s why male torties are so rare. It would be like finding a unicorn! Often, if they do exist, they may be infertile. But I think a breeding male once existed in the UK?? Which would have been a mutation, but still very very cool.

So also, I think I forgot to say earlier... the capital and lowercase letters (e.g. A/a) always denote the dominant and recessive alleles.

The next thing is the dilute modifier gene (D/d). All 3 of our cats carry one copy of this gene, which codes for melanophilin. It affects the deposition of pigment in the hair. It is a recessive homozygote, which means the cat will only show this phenotype if it carries both d/d (both recessive alleles). The black base colour dilutes to blue, and the red base colour dilutes to cream. If the cat only carries one copy of the recessive allele D/d, then those cats do not show any dilution to their coat colour, but they can pass it on.

As I mentioned, all three of our cats carry 1 copy. Therefore, none of them actually show the blue dilute colour (which is the dilution of the black base) but together, they can pass it down, and we could get blue kittens.

So, if the father and mother each pass a copy down, a baby could receive one or both of these copies.

One copy (D/d) = black kitten

Two copies (d/d) = blue kitten

Finally, here's a bit about the Agouti gene. This one is also dominant. The cat only needs one copy of the allele to show this phenotype (A/a). It means they display a tabby pattern. This is caused by alternate banding of dark and light pigment on the hair shaft. It can be both eumelanistic (black-based) or phaeomelanistic (red-based). Hence the tabby stripes.

Henley is a ticked tabby, which means he has more of a "brushed" look over his body and still has stripes on his legs and chest.

Nico has a classic tabby pattern, some regions called it a ‘blotched’ tabby or describe it as a ‘butterfly’ pattern.

On the other hand, Adelaide does not have tabby banding/stripes. This is because she carries two copies of the recessive gene (a/a), and therefore she's classed as non-agouti, or simply, she has a solid coat colour.

To make things even more confusing, both Henley and Nico only carry one copy (heterozygous) for the Agouti gene and one copy for the recessive non-Agouti gene. It looks like this: A/a. That means they can each throw a solid coat baby – BUT only if paired with another cat who can also throw down a copy.

If it were instead to look like this: A/A, where both alleles are dominant (homozygous) and two cats were paired together like so: A/A + A/A then genetically, it wouldn't be possible to throw a solid coat, all babies would be tabby.

All in all, our cats are summarised as follows:

Henley: AaDdIi  (displays tabby, carries solid, displays black, carries dilute, displays silver)

Nico: AaDdIi  (displays tabby, carries solid, displays black, carries dilute, displays silver)

Adelaide: aaDdIi  (displays solid, displays black, carries dilute, displays smoke).

I did classify them as a hetero carrier of the inhibitor gene, as there's really no way to tell what they genetically carry for this particular gene. But as I mentioned earlier, they will throw it either way. 

You can see their pairings in the Punnett Squares that I drew up. It’s easy enough to load it into an online calculator, however, it only spits out the genetic variations. So it can look kind of meaningless.

I spent some time converting it to the actual colours that are possible, and also what each kitten could carry (which means they carry the gene for it, but don’t show it in their coat colour, a bit like how all our cats carry the dilute gene, but none of them are blue).

It’s crazy how many variations can occur, and you really have no way of telling what will be created until they are born, right there in front of you!

To put it simply, both pairings (Henley + Nico  /  Henley + Adelaide) will produce a mixture of:

Black or blue solid (with or without smoke)
Black or blue tabby (with or without silver)

Nico will have a higher chance of producing tabbies, whilst Adi will have about a 50/50 chance of having solids vs tabbies. 

I'm so keen to find out what their first litters will be. 

We are looking at bringing some red into our lines, and I’m really excited about that – but that’s a story for another day!

Rosie xx

Picture references: messybeast.com