Cat Genetics Part Five - Coat patterns and matings
This is part of an ongoing series on cat genetics. If you have not yet read parts one to four, it is strongly recommended that you do so before progressing. It is important that you understand how DNA, genes, inheritance and colour work before continuing.
As well as coming in many colours, cats also possess a plethora of coat patterns, some much more complex than others. This article will give a basic overview of the most common patterns breeders work with, but it is not designed to be an exhaustive research. Many of the patterns are influenced phenotypically by complex polygenes, and significant further reading will need to be undertaken if the reader expresses a keen interest in a particular pattern. This article is designed to give a general overview with specific reference to inheritance.
Colour point, sepia and mink
These patterns are most commonly noticed in pedigree cats, although it is not unheard of for a moggy to very occasionally produce pointed offspring. These three patterns come about due to mutations on the same locus, i.e., the same part of a gene. The normal C gene, i.e. the dominant, will mean that the cat is solid coloured. The other mutations are regarded as recessive, so the cat will either possess one copy and be termed a carrier, while phenotypically remaining unaltered, or will have two copies, in which case the coat pattern will change. Cs is the code for the colourpoint gene, and this gives the cat the appearance of having darker legs, face and tail, with a light body coat. The cb mutation, also called sepia, leaves the cat with quite a dark body coat, and only slightly darker points.
If a cat possesses one copy of cs and one of cb, the phenotype appears in between that of the pointed and sepia cat, in that the offspring will have a mid-range body coat with darker contrasting points.
The expression of the phenotype is temperature controlled, with cooler portions of the body expressing more pigmentation, thus appearing darker.
Tabby
Tabby is quite a complex coat pattern, relying on the interaction of a number of different genes, the first of which is Agouti. This gene is dominant for phenotype expression, and controls the migration and deposition of black pigment into the hair shaft. It allows for banding of black and yellow pigment throughout the hair length. If a cat has two copies of the dominant, all offspring will be tabby, regardless of whether the cat mates with a tabby or not. If only one copy is present, the cat will still appear tabby but can produce non-tabby offspring. If the cat is recessive for agouti, then they cannot produce tabby offspring unless mated with a tabby, and will show no evidence of tabby markings.
It is prudent to note that the effectiveness of agouti on red pigment is limited, so red cats with no dominant agouti gene can still sometimes show tabby striping due to the tabby patterning genes.
Although agouti is the initial tabby gene, it does no more than decide whether tabby patterning will be visible. Further mutations code for different tabby patterns, and it is postulated that all cats have these genes, but that they are mostly hidden by the absence of the dominant agouti. Ticked tabby (Ta) is a dominant patterning, as is the Mc gene which expresses mackerel tabby. Mc codes for classic tabby patterning. There is further debate on the possible existence of a spotting gene which breaks up the solid stripes of non-ticked tabbies to produce a spotted pattern, but research is still ongoing.
Solid
Solid is the term used to denote a cat who is of a uniform colour with no coat pattern, and has been covered in the previous articles regarding colour. However, it is prudent to note some facts.
Black tends to predominate due to the fact that it only requires one copy of B to express in phenotype. Red is less dominant as it is sex-linked. Chocolate and cinnamon are rare due to needing two copies to express. Blue, cream and fawn need two copies of the dilution gene to be seen. Caramel colours are perhaps rarest of all, as not only do they need two dilution genes, but they also then need the dilute modifier to express.
Mating
It is important to be able to predict coat colour and pattern when deliberately mating two cats. In order to do this accurately, you first need to know what recessives the cat may carry. You then need to be able to construct and deconstruct phenotypes to genotypes. To aid this, some examples are given below. The simpler explanation of colour will be used to aid all readers in understanding, but for all intents and purposes, the processes involved are the same. Scientific types will simply need to deconstruct and construct one step further to remove the Phaeomelanin gene to get black.
Deconstruction
This is perhaps the easier skill to learn, as the phenotype is clear, therefore deconstruction is logical. Deconstruction is a term which encourages the removal of known genes to reduce a phenotype back to base colours. It is important as it allows you to see what a cat is using to produce a phenotype, and thus, what it may pass on to offspring.
As an example, consider a blue tortie tabby colourpoint. Bearing in mind that the base colours are black and red, the breeder must ask themselves how we can regress the cat’s phenotype to this status. First, remove colourpoint. This would give a phenotype of a blue tortie tabby. Next, remove tabby. This leaves the cat as a blue tortie. Remove dilute, and the cat becomes a tortie. Torties are black and red, therefore, you have reached your base colours.
If the same is done with a chocolate mink, you would remove one copy of cs and another of cb to give a chocolate solid. Remove chocolate to get black. And thus, you have reached your base colour.
Construction
This is the opposite of deconstruction, in that you add genes in order to get the desired phenotype. It is important because, by doing this, the breeder is able to anticipate what the parent cats will need to carry or express in order to pass it on to offspring, and subsequently select for that in their breeding programme. It also allows for the omission of undesirable traits.
Your desired phenotype is a cream tabby bi-colour. You would therefore begin with a red cat, as cream, the base colour, is a dilute of red. Add the white spotting gene and your cat is now a red bi-colour. Add tabby and the cat is now a red tabby bi-colour. Add dilute, and your phenotype changes to a cream tabby bi-colour.
Your desired phenotype is now a lilac tortie sepia. Begin with a tortie cat. Add chocolate and your cat becomes a chocolate tortie. Add dilute and she becomes a lilac tortie (remember that lilac is the dilute of chocolate). Add two copies of the cb gene and she becomes a lilac tortie sepia.
But how does that help me predict colours
When you choose two cats to mate after constructing or deconstructing their phenotype, you will have a very good idea of what qualities they add to the genetic mix. When you have this information, you are able to use it to construct all possible resulting phenotypes when the two are combined, but in order to do that, you need to know which colours and patterns are dominant and which are recessive.
As an example, consider mating a blue tortie tabby who has only one copy of the tabby gene and carries colourpoint and dilute, to a chocolate colourpoint also carrying dilute. Attempt to predict possible colours and patterns for boy and girl kittens (remember that red and red variants are sex-linked).
Outcome
There is an even chance of having tabby and non-tabby kittens, as mum holds one copy of the tabby gene.
There is also an even chance of colourpoints as dad will definitely provide a copy to offspring (colourpoint is recessive, therefore dad has two copies as he is phenotypically a colourpoint, and so must give one to each kitten), and mum has one copy. Therefore, mum will decide whether kittens are colourpoint or not. All non-colourpoints will carry 1 copy of the colourpoint gene.
As both parents carry dilute, there is the possibility of dilute phenotype babies. Even the darker coloured kittens could carry dilute.
There is no possibility of chocolate phenotypes as mum does not carry it, but all kittens will be chocolate carriers as dad will give each kitten a copy.
Boy kittens could be black, blue, red or cream, and can be tabby, colourpoint, both or neither. Note that, if a cat is pointed, black is referred to as seal, as the pointed gene changes the colour slightly.
Girls can be black, blue, black tortie or blue tortie, again either tabby, colourpoint, both or neither.
Remember that red is sex-linked.
It is self-evident that breeding cats is, or can be, quite a scientific undertaking for any breeder, and further research into genetics specific to the chosen breed is strongly recommended. Each breed has its vagaries and quirks, and a true understanding can only be gained with the seeking of further specific knowledge.
Cat Genetics Series
