Free Feline Colour Genetics Course – Module 1

Feline colour genetics course

Module 1 – Basic genetics theory, solid colour cats and the dilute gene

Introduction

The subject of genetics can seem somewhat daunting if you have never delved into it before but I promise you once you get the basics under your belt, the pieces of the puzzle will all click into place and you will wonder what all the fuss was about! It is a great subject to learn about and a basic understanding of genetics is vital to any breeder and should play a vital role in deciding which cats to pair together.

Understanding genetics can help us eradicate as far as possible, undesirable traits; be they a conformational fault or something more sinister such as predominance to certain diseases or conditions. It can also help us breed for desirable traits such as a particular colour or positive physical or healthy attributes. It goes without saying that the first and foremost priority in any responsible breeders plan should be health above all. There is also a great deal of work done by breeders through careful selection to develop new breeds and preserve older breeds and indeed genetics plays a vital role in this also.

In this course which will run over several modules we shall take a look at feline colour genetics to help you in your breeding effort. Though we will be focusing on colour genetics, many of the same principles will apply to other genes, however; you should research each gene you are considering so that you understand the way in which it is passed on.

I hope that this course helps you to better understand how certain traits are passed on and allows you to make more informed choices in your own breeding program so that you can truly strive to breed healthier and better quality cats. Also if you do not breed but are interested in this fascinating subject then I hope you find it both enjoyable and informative.

Each course module will give you a basic overview of the module subject and will have short exercises throughout for you to complete to help make sure you understand what you are learning so far. The answers will be given at the end of the module so you can check your work.

At the very end of the entire course there shall be a short quiz covering all the topics discussed during the entire course. Don’t worry, it is not an exam! You can answer the questions in your own time to test yourself and see how much you learned and if there are any areas you might like to recap on. No one will know your results, they are for you and you alone but if you wish to share your results with us on our website or give us any feedback you will be more than welcome and we’d love to hear how well you’ve done and if you enjoyed the course. At the bottom of every module will be a comments box so you can make comments or share your experience of the course.

This first module may well be the toughest simply because it has so much to cover to give you a solid foundation but after that things get far easier!

Please note: This is a fun course designed for those with an interest in learning more about feline colour genetics and does not result in a qualification of any kind. It is not meant to take the place of education from a qualified professional and we encourage you to research thoroughly into any information you find on the internet before you act upon it.

 

With that all said, let’s get started…

 

1.1 – Basic genetics and how different characteristics are passed on

Our genes dictate how our bodies are made up right down to the very last cell and the same goes for our cats. Genes are passed down from the parent cats to their offspring and are made from DNA(Deoxyribonucleic acid).

Here we can see the structure of DNA strands and how strands of DNA come together to form chromosomes, which in turn can be found in the nucleus of cells.

Short strands of DNA group together to form a chromosome which can be found in the nucleus of cells and holds information to tell the cells how to develop, what characteristics to display and which ones to hide. Chromosomes are always present in pairs with the exception of sex cells i.e. sperm and eggs. This is because when sperm and eggs meet they create a pair of chromosomes between them.

 

Male vs female

As we know, every cat has two chromosomes. One inherited from its’ mother and one inherited from its’ father. Chromosomes can be either an ‘X’ chromosome or a ‘Y’ chromosome. Females always have their pair of chromosomes made up of two X chromosomes written as ‘XX’ and males always have their pair made up of an X chromosome and a Y chromosome so theirs is written ‘XY’. Since a female has two X chromosomes she can only pass on X chromosomes to her offspring and a male can pass on either an X or a Y chromosome to his offspring.  We can see from this that is the male which determines the sex of the kittens since a female can never pass on the male Y chromosome as she doesn’t have it present in her genes.

Various traits that each parent has reside on these chromosomes. Colour lays on the X chromosome and so for this reason a male kitten will always get his colour genes from his mother since his father will have only passed on a Y chromosome to him and his mother will have passed on an X chromosome (where colour genes live). We shall discuss this in more depth in a later on in the course as not every gene that affects colour resides on the X chromosome.

 

1.2 The different colour genes of cats

Really when we break everything down to basics there are only two colours of cats. Yes, only two! …Red cats and black cats. Every other colour is a modification/mutation of the red gene or the black gene and/or the addition of a gene that alters or masks the main colour of the cat.

The different genes are written by symbolising each with a certain letter. This allows geneticists to document what genes a cat has which physically show up and also what genes it carries that are not visible on the cat, all without having to write a lengthy description – we call this the genotype.  When we describe the observable physical characteristics of a cat or kitten we refer to this as the phenotype.

The definition of genotype and phenotype as printed in the oxford English dictionary are as follows:

 

genotype

NOUN

Biology 

  • The genetic constitution of an individual organism.

Often contrasted with phenotype.

 

phenotype

NOUN

Biology 

  • The set of observable characteristics of an individual resulting from the interaction of its genotype with the environment.

 

1.3 Dominant and recessive genes and how they work

Each gene can have multiple alleles (pronounced Al-leels). Alleles are when the same gene has different characteristics, such as the gene for eye colour in humans can have an allele for brown eyes and allele for blue eyes.

Some alleles are dominant and some are what is known as recessive. When a dominant allele is present in the genetic make-up of a cat then this characteristic will be the one that is physically observable and the recessive allele will not be observable but will still be present in the genetic make-up. In this instance we call this cat a ‘carrier’ of whatever gene it has in its genetic make-up but does not physically show.

An easy example of how dominant and recessive genes work would be to look once again at eye colour in humans: Brown eyes are dominant over blue eyes. If a brown eyed person who did not carry the allele for blue eyes had a baby with a blue eyed person then the baby would have brown eyes because brown is dominant over blue. It would still carry the allele for blue eyes but it just wouldn’t be observable. This baby would be a brown eyed person and a carrier of blue eyes.

So how does this work? Dominant alleles need only one copy of themselves to be present in the genetic make-up to be physically observed. A recessive allele needs two copies to be present to be physically seen. Since one allele will come from each parent then both parents must either have blue eyes or carry the allele for blue eyes for their child to have blue eyes.

When discussing the colours of cats’ red is the most dominant colour gene found in cats. Black, while also a dominant colour gene, it is recessive to red but dominant over all other mutations. Mutations are permanent alterations of DNA sequences which are different to what is considered normal for a particular gene. Green eyes in humans are an example of a gene mutation.

 

1.4 All about melanin

Melanin is responsible for pigment and is made up of microscopic granules of varying shape and size. It is what produces colour in hair eyes, skin etc. There are two types of melanin which a cat could have depending on its genes: pheomelanin and eumelanin. The red gene (which will be covered in more detail later) results in a cat having pheomelanin and the lack of red gene leaves a cat with eumelanin and therefore black in appearance.

Pheomelanin granules are thought to be long and sausage shaped and cause light to be reflected in the yellow and orange ranges while eumelanin granules are believed to be spherical and as such absorb the vast majority of light leaving us with the appearance of black. So to summarise, a cat will either be red or black before it is anything else.

 

1.5 Red cats – a basic overview

The red gene in cats is what makes cats ginger and also contributes to the tortoiseshell colour sometimes seen (tortoiseshell will be discussed in its’ own section later on in this module). As we already know red is dominant over

A red cat, otherwise known as ‘Ginger’.

all other colours and resides on the X chromosome. This makes red a sex linked trait. This is because as we discussed earlier, a male can only pass on his X chromosome to female kittens as he passes on his Y chromosome to male kittens thus making them male. As red resides on the X chromosome it is impossible for a male cat to pass on any sex linked gene to his male offspring. Male kittens get their X chromosome from their mother. If their mother is black then the male kittens will all be black. If the mother is red then all the male kittens will be red.

As mentioned earlier, genes are symbolised by letters for easy interpretation of genotypes when written on paper. Red is symbolised by the letter ‘o’ (for orange).

A capital ‘O’ means that the cat has the red gene present in its’ DNA. If a cat has red present in its’ DNA then it would display red in its phenotype as red is a dominant gene. We use capital letters to symbolise dominant genes. Use of a lower case ‘o’ would mean the cat does not have the red gene present on that chromosome.

A cat can never carry red because red is the most dominant gene of all so if a cat isn’t physically observable as being either red or tortoiseshell then it does not have red in its genotype and will never pass on the red gene to any of its’ kittens. Its’ genotype would therefore be: ‘oo’. If a cat was physically observable as being red it would have a genotype of either ‘OO’ or ‘Oo’.

 

1.6 Black, Chocolate and Cinnamon cats

 

Black, like red is a dominant gene; it is symbolised by the letter B. Although it is recessive to red, because it is the most dominant of the black based colours it is always symbolised using a capital B. The genotype of a black cat would be written as ‘BB’.

A black cat has the genotype ‘ooBB’

 

Chocolate is a mutation of black that turns the black pigment to brown. It is recessive to black meaning that a cat would have to have two copies present in its’ DNA for the trait to show.

Oriental havana: a genetically chocolate cat. For picture credits please see the end of the module.

A chocolate cat as its name describes, is usually milk chocolate brown in colour though some may be darker. Because chocolate is recessive to black yet still part of the same gene we still symbolise chocolate by using a letter ‘b’ but instead of a capital ‘B’ we use a lower case ‘b’. The genotype of a chocolate cat that does not carry any other colour mutation or alleles would be written as ‘bb’. When a cat has two copies of a certain gene such as ‘BB’ or ‘bb’ we describe them as being homozygous for that gene. So ‘BB’ would be homozygous black and ‘bb’ would be homozygous chocolate.

Cinnamon is another mutation of this gene and is recessive to both black and chocolate. Cinnamon cats, like chocolate cats need two copies

Oriental Cinnamon: b1b1, recessive to both black and chocolate. For picture credits please see the end of the module.

of the gene present to appear cinnamon. Cinnamon cats are a light cinnamon brown in colour. When writing cinnamon, since we cannot go lower that a lower case ‘b’ we refer to cinnamon as ‘b1’. A cinnamon cat which must be homozygous for cinnamon to appear cinnamon would be written as ‘b1b1’.

All of these cats would have ‘oo’ in their genotype as they are not red. A homozygous black cat would have the genotype ‘ooBB’ which translates to: a cat that does not have red present in its DNA and has two copies of black meaning it will therefore have a phenotype of black.

 

1.7 Carriers and heterozygous

 

So what would happen if we mated a black cat to a cinnamon cat? All the kittens would receive the black gene and a copy of the cinnamon mutation but because black is dominant over cinnamon then all the kittens would appear black. They would still have cinnamon present in their DNA but it just wouldn’t show up in their phenotype (appearance). A cat or kitten that appears one colour but has another colour hidden in the DNA like the kittens from the Black to Cinnamon mating described above are referred to as ‘carriers’ or ‘heterozygous’.

The results we would see from a homozygous black cat mated to a homozygous Cinnamon cat

Similarly if we mated a chocolate cat to a cinnamon cat we would have a litter of chocolate kittens that all carry cinnamon. The genes for the recessive trait such as cinnamon would be present but unable to show because chocolate is dominant over Cinnamon.

Since cinnamon is recessive to both chocolate and black we know that a cinnamon cat can never carry either of these genes as if it had a copy of either of them present in its’ genotype then that would be the colour that we would see displayed in the physical appearance of the cat. The kittens resulting from a cinnamon to cinnamon mating would all be homozygous cinnamon (b1b1).

The Cinnamon mutation resides on the same locus (location on the chromosome where the particular gene is found) as chocolate and so a black cat cannot ever carry both chocolate and cinnamon. It can only carry one or the other.

This ability for genes to be carried but not exhibited is why sometimes a surprise colour can appear in a litter of kittens. If two black cats are mated but each of them is a carrier of chocolate then 75% of the kittens would be black and 25% would be chocolate. Quite a surprise to get a gorgeous chocolate kitten in a litter of black kittens!

Cats that are carriers of certain genes have their genotype written to account for the hidden or masked gene. For example a black cat carrying chocolate will be written: ‘ooBb’

A chocolate cat carrying cinnamon will be written ‘oobb1’

Often, in working out genetic colour predictions, if neither of the parents are red or any variation of the red gene then the ‘oo’ will be omitted from the written genotype as we know that if a cat does not show red it will not carry it and therefore cannot pass red onto its kittens. In this case you may wish to write a black cat as ‘BB’ as opposed to ‘ooBB’ as red will always be zero so there is no need to write it down. This of course would not be wise in a mating in which one or both parents had the red gene.

This clearly shows each gene that the cat has present in its DNA but as we know which ones are dominant we know which ones the cat will display.

 

Exercise 1

We have created a worksheet with all the exercises for module 1 detailed on them so all you have to do is fill in the answers. You can access it and print it out by clicking the link: Feline colour genetics course m1 worksheet

M1.E1: Below are 4 cats each with their genotype written beside them. Based on what you have learned so far and from the details given in the genotype for each cat, see if you can work out what phenotype each would be and which colour (if any)each one carries…

Cat a) ooBB appears:__________________& carries:___________________

Cat b) oobb1 appears:_________________& carries:____________________

Cat c) oobb appears:__________________ & carries:____________________

Cat d) OObb appears:_________________& carries______________________

 

1.8 Punnet squares – How to determine litter probabilities on paper

Exercise 1 and all this talk of various genes being recessive or dominant to one another and homozygous and heterozygous may have got you thinking.

When we start dealing with carriers combined with various recessive alleles etc. it gets a little trickier to predict the outcome by working it out in your head. This is where the punnet square comes in. The punnet square is a simple tool used to make our lives easier and take the complications out of colour predictions and which genes will be carried by kittens in the litter.

A punnet square is a grid that represents the two chromosomes passed on by both the dam (mother) and the sire (father) and shows what approximate percentage of the litter will be of a certain genotype. In these punnet squares we are using today each of the results squares which are highlighted green represent 25% of the resultant litter.

Let’s look at how a punnet square is written and filled in to illustrate the expected results of a homozygous black male cat (ooBB) mated to a homozygous chocolate female cat (oobb).

This is an empty punnet square with the different areas highlighted to help you understand what information goes in which box.

The genotype of the male is always written in the top boxes which have been highlighted in blue and the genotype of the female is always written in the side boxes which have been highlighted pink. As neither cat has the red gene present in their genotype we shall omit ‘o’ from our punnet square and prediction as we already know that 0% of the kittens will be red.

This means our male will have a genotype of ‘BB’ and our female will have the genotype ‘bb’.

Our punnet square with both the parents genotypes filled in will look like this…

To work out what genotype our kittens would be if we mated these two cats together we simply copy the letter (in this case ‘B’) from each of the father’s alleles into each box below it and copy the letter (in this case ‘b’) from each of the mothers alleles into each box across from it. This leads to all four of the results boxes having an allele from the mother and an allele from the father present, thus using the two genes from each parent needed to make up a pair of chromosomes. Capital letters are always written first.  Once this has been done it should look like this…

As you can see from the punnet square above all of the resulting kittens all have the genotype ‘Bb’ meaning that 100% of the litter would be black in appearance but each carry the chocolate gene.

 

1.8a Heterozygous to heterozygous matings

Now what if we mated a male black cat which was heterozygous for (carries) chocolate (Bb) to a female black cat who was heterozygous for chocolate (Bb)? Firstly let’s put our parents’ genotype into the punnet square. It should look like this…

Next we shall put in the letters that represent our male’s genotype in into the results squares…

 

And now the letters that represent genotype of our female and what she will pass onto their kittens…

As we can see 25% of the kittens will be black (BB) and will not carry chocolate – they will be homozygous black. 50% (two of the four boxes) of the kittens will be black and carriers of the chocolate gene (Bb) – they will be heterozygous for chocolate and 25% of the resulting kittens will be chocolate (bb) – they will be homozygous chocolate.

We know that 2/3 of the black kittens will carry chocolate but it will be impossible to know which ones they are just by looking at them.

 

Exercise 2

M1.E2: Below are two punnet squares which have had the parents alleles already filled in for you. See if you can fill in the results of the next two punnet squares for yourself and from your results determine the answers to some simple questions about the kittens.

If you have not yet printed off our worksheet, you can do so here: Feline colour genetics course m1 worksheet

If you need extra working out space/ punnet squares to practice on you can either scribble a copy of the punnet square down onto some scrap paper or alternatively you can print off our free blank punnet square by clicking the link below and then fill in the information you need.

Punnet squares PDF (free blank punnet squares work sheet for your use)

Punnet square a)

 

  1. Write down the different genotype/s that appeared in this litter?______________________________________
  2. What phenotype were the kittens?_____________________________________________
  3. What percentage of kittens were homozygous chocolate?__________________________
  4. What percentage of kittens were homozygous black?_______________________________

Punnet square b)

1. What genotype would the kittens be? (this time include percentage such as 50% bb and 50% BB as applicable to this punnet square)___________________________________

2. What phenotype would the kittens be?__________________________________________

3. What percentage of kittens would be heterozygous for chocolate?____________________

4. What percentage of kittens carried black in their genotype?______________________

Well done on completing and reading your first punnet squares! Did you spot the trick question!!! 😉

In the above exercise we only covered black and chocolate to keep things easy. Now lets’ have a go at looking at adding the cinnamon mutation into the mix. We know cinnamon is recessive to chocolate and a cinnamon cat is written as ‘b1 b1’. Since cinnamon is recessive to both black and chocolate a cinnamon cat can never carry either black or chocolate.

 

Exercise 3

M1.E3: Just like in exercise 2, see if you can fill in the punnet squares below and answer two simple questions about each one.

Punnet square a)

  1. What phenotype would the resulting kittens be?__________________________________
  2. How many kittens would be black?_____________________________

 

Punnet square b)

  1. What percentage of kittens would be cinnamon?______________________________
  2. What percentage of kittens would carry cinnamon?____________________________

 

Punnet square c)

  1. What percentage of kittens would be heterozygous for chocolate?______________
  2. How many different phenotypes would we see in this litter of kittens?__________________

 

How did you get on? Hopefully you should be feeling a bit more confident now and fingers crossed you are enjoying learning something new and had fun with some of those trick questions that get the cogs turning a bit more.

Below is a quick summary of the genotypes for black and its mutations. For your convenience both heterozygous and homozygous combinations have been included as well as a picture of what the phenotype would be.

Homozygous Black= BB – this cat or kitten would look black and does not carry either chocolate or cinnamon.

Black carrying (or heterozygous for) chocolate = Bb – this cat or kitten would be black in appearance but carry the chocolate mutation which it could pass onto its’ kittens.

Black carrying cinnamon = Bb1 – this cat or kitten would be black in appearance but would carry cinnamon which it could pass onto its’ kittens.

 

 

Oriental havana: a genetically chocolate cat: either bb or bb1. For picture credits please see the end of the module.

Homozygous chocolate = bb – this cat or kitten would look chocolate in appearance and would not carry cinnamon and could not carry black since black is dominant over chocolate. If mated to a cinnamon cat then all the kittens would be chocolate carrying cinnamon since chocolate is recessive to cinnamon.

Chocolate carrying cinnamon = b b1 – this cat or kitten would appear chocolate but carries the cinnamon mutation. If mated to a cinnamon cat or another chocolate carrying cinnamon cat then they would produce a mixed litter consisting of some cinnamon and some chocolate kittens in both instances.

 

Oriental Cinnamon: b1b1, recessive to both black and chocolate. For picture credits please see the end of the module.

Homozygous Cinnamon = b1 b1 – this cat would be cinnamon in appearance and can never carry chocolate or black since these are both dominant over cinnamon. For any cat to be cinnamon it must have two copies of this allele present in its genotype.

 

Don’t forget to grab a break if you need one! 🙂

 

1.9 Tortioseshell  and how sex linked genes are predicted

So if red is dominant over all genes then how is tortoiseshell produced? Would the red not simply be dominant over black leaving a red cat carrying black? The answer to this is no and here’s why…

Tortoiseshell cats are usually always female

…The secret lays’ with the X chromosome. We know that male kittens can only get their colour from their mother but that female cats will have a combination of colour from both their mother and their father because she will receive one X chromosome from her mother and one from her father whereas the male will receive a Y chromosome from his father which does not carry colour genes but in turn makes him male.

As red is the most dominant colour, if a red male mated to a black female then all the female kittens would inherit red from their fathers X chromosome. Red, being the most dominant colour would be displayed. She would also inherit a black X chromosome from her mother and since black is also a dominant gene and the female has the ability to have two dominant colours present since she has two X chromosomes she will display red on one chromosome and black on the other. This means that all the female kittens from this litter would be tortoiseshell. All the males on the other hand cannot receive an X chromosome from their father and so receive it from their mother making them all black. Each male kitten in this litter would be black.

We can see this more clearly if we put the information into a punnet square…

In this punnet square we can see the red gene symbolised by an orange X in the male’s genotype. We know that red cannot be passed on with the Y chromosome and we can clearly see that the female kittens which each have two X chromosomes all have both a red X chromosome and a black X chromosome, thus making them tortoiseshell.

What happens if we mate a tortoiseshell female to a red male?

After filling in the relevant information we can see that male kittens would have a 50% chance of being either red or black and female kittens would have a 50% chance of being either red or tortoiseshell. Contrary to popular belief it is very possible to have a red female and she is not sterile. On the other hand it is very rare to have a male tortoiseshell. For a male to be tortoishell he needs to have an extra X chromosome which would make him have XXY. This would allow him to be tortoiseshell but would invariably make him sterile. The odd one has cropped up but it is extremely rare!

Tortoiseshell cats can get even more interesting!

A tortoiseshell cat can be a black tortoiseshell, a chocolate tortoiseshell or even a cinnamon tortoiseshell. This is because both the red and black genes will show but if the black part of the genetic make-up is ‘bb’ for example then this would be a chocolate cat and thus the addition of the dominant red gene ‘O’ would make the cat chocolate tortoiseshell.

 

Exercise 4

Now onto some punnet squares which include the red gene…

M1.E4a: The punnet square below is already filled out for you in entirety. Both X and Y chromosomes have been included alongside the colour alleles so that you can clearly see how the colour of red correlates to the X chromosome. Using the completed punnet square, try to answer the two questions below.

  1. The punnet square tells us that we have a red male mated to a homozygous black female. What percentage of the kittens in the litter would be tortoiseshell?______________.
  2. What colour would the female kittens be?_____________________.

 

M1.E4b: Below is another punnet square with the genotypes of the parents already filled in for you. Fill in the remainder of the punnet square and see if you can answer the questions that follow.

  1. What is the phenotype of the mother and father used in this punnet square? Mother:___________________Father:______________________.
  2. What percentage of kittens would be red? ___________________.
  3. Some of the male kittens resulting from this mating would be red and some would be black. True or false?
  4. From this mating, what percentage chance would a kitten have of being a red female?______________.

 

A quick recap before moving onto the final part of this module…

Let’s recap on what we have learned so far. Below is a checklist for you to use to make sure you are ready to move onto the next module. Check off anything you know and anything you are not sure on skip back to the relevant part of the module to brush up of your genetics knowledge.

 

Learning checklist…

  • Each parent has two chromosomes and each kitten receives one chromosome from its dam and one from its sire.
  • Dominant genes or alleles will show themselves over a recessive gene/allele so a cat can still produce kittens of the recessive colour if it is mated to either: another cat displaying same recessive gene or a cat who appears to be a dominant colour but that still carries a copy of the same recessive gene.
  • Genotypes are written as letter with capital letters representing dominant genes and lower case letters representing recessive genes.
  • I know what a punnet square is and how to both complete one and read one on a basic level.
  • I know the written genotype for Black, chocolate and cinnamon like it was tattooed on the backs of my eyelids!
  • I know that black is dominant over chocolate and cinnamon, that chocolate is a recessive gene mutation that is recessive to black but dominant over cinnamon and that cinnamon is recessive to both black and chocolate.
  • I know that red is the most dominant colour gene and that it resides on the X chromosome.
  • I know that because a male gets his X chromosome from his mother that he also gets his colour from his mother – either black or red.
  • I know and understand what a carrier is.
  • I understand what is meant by the terms: chromosome, gene, allele, locus, genotype, phenotype, homozygous and heterozygous.
  • I know that for a recessive trait to show in the physical appearance of a kittens in any given litter then both the parents must either be a carrier of that trait or visually display it.
  • I know that a cat which has a cinnamon phenotype and is therefore visibly cinnamon in colour must be homozygous for cinnamon.

…Ok so far?

Don’t forget to take a break if you need to! Brain power can be exhausting and it is easier to learn when you are feeling fresh. If you are completely new to genetics the first part can seem like a bit of a minefield but you will get there in the end, I promise! This first module is the largest and the most difficult but stick with it and you will do amazingly!

 

1.10 The Dilute gene

If you are ready let’s move onto the last part of this first module and explore the dilute gene which is responsible for those gorgeous cream, blue, lilac and fawn cats!

The dilute gene is an autosomal recessive gene. ‘Autosomal’ means that it is not carried on the X chromosome and so unlike the red, a male cat can pass this trait onto both his male and female kittens, and so can the female.

This gene lightens the original coat colour of the cat so that it is a diluted version of its actual genetic colour. Visually, it is a bit like if you were to add lots of water to thick black paint until the paint turns thin and appears lighter than if you hadn’t added the water. It is believed that this is due to the grouping and clustering of the pigment granules.

The fact that dilute is a recessive gene means that like the recessive colour mutation Cinnamon, to show a dilute colour the cat must have two copies of the gene present in their genetic make-up. If they only had one copy they would carry the gene but not show it. This means that for a kitten to be one of the dilute colours its parents must either be dilute or carriers of the dilute gene.

The dilute gene does not remove the original colour gene but rather it changes its’ appearance.

The dilute gene is represented by the letter ‘D’. Capital ‘D’ means no dilute gene is present and a ‘d’ means there is dilute. A genotype of ‘DD’ is  not dilute and does not carry dilute. A genotype of ‘Dd’ is a carrier or heterozygous for dilute and a genotype of ‘dd’ is dilute and will display the dilute version for its’ genetic colour.

How the dilute gene affects each colour

So what do each of the colours we discussed look like when dilute is added to the mix? For ease of learning none of the cats in this section are carriers of any other genes.

A red cat that carries two copies of the dilute gene and is therefore homozygous for dilute then becomes cream. Genotype OOBBdd

 

 

 

A black cat which is homozygous dilute becomes a blue cat. Genotype ooBBdd

 

 

 

A chocolate cat which is homozygous dilute becomes a lilac cat. Genotype oobbdd.

 

 

 

A cinnamon cat which is homozygous for dilute becomes a fawn cat. Genotype oob1b1dd

 

 

 

Tortoiseshell and dilute…

Blue cream tortie (OoBBdd)

A tortoiseshell can also be dilute and when this happens you will end up with the following:

A regular black and red tortie will become a blue cream tortie. Genotype OoBBdd.

A chocolate tortie will become a lilac cream tortie. Genotype Oobbdd.

A cinnamon tortie will become a fawn tortie. Genotype Oob1b1dd.

Many of these dilute tortoiseshell cats are very striking and breathtakingly beautiful!

 

The genotypes for the three black based dilute colours are:

Blue phenotype = genotype of  BBdd or Bbdd or Bb1dd

Lilac phenotype = genotype of bbdd or bb1dd

Cinnamon phenotype = genotype of b1b1dd

When we fill in punnet squares we can do this in exactly the same way as we did with the colour of the cat.

For example a Blue male which is homozygous for black as well as homozygous for dilute (BBdd) mated to a cinnamon female that carried dilute (b1b1 Dd) would look like this…

From this we can see that 50% have the genotype Bb1,Dd which would be Black carrying both cinnamon and dilute and the remaining 50% would be Bb1,dd which would be a genetically black kitten that carried cinnamon and were homozygous for dilute thus making their phenotype Blue.

As with the genes they are based on, cream is the most dominant of the dilute colours since it s a dilute version of red which we know to be the most dominant colour gene found in cats. Blue is the next most dominant of the dilute colours and is dominant over both lilac and fawn. Just as with cinnamon, fawn is recessive to all other dilute colours.

A non-dilute version of a colour will always be dominant over the dilute version so if you have a fawn can and mate it to a cinnamon cat then the babies will all be cinnamon and carry the dilute gene that enables fawn kittens to appear in a litter.

Exercise 5

M1.E5: Below are three questions for you to answer. Based on your knowledge of the dilute gene try to answer them correctly…

  1. If a blue cat is mated to a black cat that does not carry any other colours and does not carry dilute what will the genotype of the kittens be? If you wish to draw out a punnet square to help you with this you can____________________________________________
  2. A Cream male and a chocolate female are mated together. What colour will the female kittens be?_____________________________
  3. A Blue cat is a dilute version of which colour?____________________________

Note: When working out dilute colours on punnet squares…If you prefer to work over two separate punnet squares for ease of reading when adding in the dilute gene you may certainly do that. You will still get the same results. You would simply fill out the colour in one punnet square and work out your results to determine what colour your kittens would be. You would then fill out a separate punnet square for the dilute alleles to determine what percentage of the kittens would be homozygous dilute and know that this dilute could apply to any of your kittens. If you know that black becomes blue, chocolate becomes lilac and cinnamon becomes fawn you will always be able to work out what colours you might end up with in any given litter.

One thing to remember with genetics is that nothing is a dead certainty. We use percentages as a rough guide. For example if we mate a black cat that carries chocolate to another black cat that also carries chocolate then we predict that 25% of the kittens will be chocolate and 75% will be black, some of which will carry chocolate but this doesn’t mean that in a litter of four you will guaranteed get 3 black kittens and one chocolate kitten. It simply means that each kitten has a 25% chance of being chocolate and a 75% chance of being black in phenotype. You may end up with 2 chocolate kittens and 2 black in a litter of four. It does give you a rough guide of what to expect and it does let you know what colours could show up.

I hope you have enjoyed the first module in this course and have found it helpful. If you have any questions relating to this module please let me know in the comments box below and be sure to let me know if you enjoyed it and found it useful. I am very grateful for any feedback both good and bad as this helps me create more of what you want to see in the future.

I look forward to going over our next module together next couple of weeks. For now, enjoy your cats and play around with punnet squares!

Click here for the furkidz.org Cat colour genetics course: module one exercise answers to see how much you learned!

Print off our free blank punnet squares sheet to work on by clicking the link below…

Punnet squares PDF

Coming up in Module 2…

Join us in 2weeks time for the next module where we shall be looking at genes responsible for white cat and cats with white markings referred to as Bi-colour cats.

Throughout module 2 we shall be looking at Albinism, white spotting gene which produces bicolour cats and solid white cats as well as how to spot a cat of a particular genetic standing i.e. a genetically white cat vs a high spotting white cat. We shall also be looking at deafness and how it relates to white.

 

Picture credits

If you wish to use any of our images or graphics used in this module please feel free but please create a link back to this site and acknowledge your use of any of our images or graphics(furkidz logo is an exception to this). Some of the images used in this module do not belong to us and were used with the kind permission from Ross of www.oriental-cat-breeder.co.uk  and these images have been listed below and include a link back to the Oriental cat breeder website. If you would like to use any of these images please visit the oriental cat breeder website and discuss it with them. Thank you Ross for sharing some of these outstanding pictures and fine examples of feline colours not to mention, some cracking orientals!

Oriental red, Oriental havana, Oriental Cinnamon, Oriental cream, Oriental blue, Oriental Lilac & Oriental fawn were all used with the kind permission of www.oriental-cat-breeder.co.uk Thank you very much for the kind sharing of images:-)

 

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