Free Feline Colour Genetics Course – Module 2

Feline colour genetics course

Module 2 – All about White cats, Bi-colour cats and the genes responsible for them

 

Introduction

Welcome back and I hope you are looking forward to beginning module 2 where we shall be looking at white and how it is passed on through the genes. White cats are truly beautiful and many people have a strong love of white cats. White is often viewed with mixed feelings since white is the colour most commonly associated with deafness, not just in cats but in other animals too.

White in cats can be caused by several types of genes and contrary to popular belief, not all white cats are deaf.

The different genes responsible for white are: Dominant white, white spotting gene and albinism.

Let’s look at each one individually and discuss their differences.

 

2.1 Albinism

Albinism is perhaps one of the most widely recognised genetic traits that results in white animals; however, it is also the rarest of cat colours. Albinism causes a cat to be white by removing colour i.e. pigment and is the most recessive colour gene to be found amongst cats.

When we think of albinism we usually think of the pink eyed albino just as we would see in traditional lab mice. This same pink eyed appearance is also true of albino cats. Their eyes will be a pinkish red and very sensitive to light; their coat will be a pure white and their skin lacking any pigment, leaving it pink. Albino cats are not usually prone to deafness. Deafness is more commonly associated with the dominant white gene which we shall discuss later in this module.

This is Smifrnoff, an albino cat. Please see the bottom of the module for picture credits.

Albino is symbolised by the letter ‘c’. An upper case letter ‘C’ means the cat does not have albinism and a lower case letter ‘c’ means the cat has the albinism gene. As albinism is a recessive gene a cat would need two copies of the gene present in its genotype to be physically observed as being albino. One copy of the gene would cause the cat to appear its usual genetic colour but it would also carry the gene for albinism which it would in turn pass onto its kittens. It would be heterozygous for albinism.

A fact often un-known to beginners in feline genetics is that the Siamese colouring that results in a colour point is also a mutation of the albino gene but we shall not discuss that in this module as it will be covered in its own module later in the course. There are actually five variations on the albino locus(C).

The five variations are:

A lilac point siamese – Siamese is one of the five variations of the albinism gene

Non albino – full coloured (C)

Burmese (cb)

Siamese (cs)

Blue eyed albino (ca)

Pink eyed albino (c)

You will see that one variation is listed as a blue eyed albino. Often people will see a cat that is white in entirety and has blue eyes and think it is albino. While this can sometimes be seen, the blue eyed albino has extremely pale blue eyes and the pupils will often still appear red as opposed to deep black. This is because light reflects off of the blood vessels in the back of the eye with no pigment there to cause any other colour. Blue eyed albino is dominant over pink eyed albino which is often referred to as true albino. This pink eyed albino is the most recessive of the albino variations.

Lets begin with our first exercise…please print off the Feline colour genetics course module 2 worksheet to use with this module. The Extra Punnet squares PDF  is also available for you to print off for this module or for your own personal use. Please click here to print off extra punnet squares. Answers will be available at the end of the module to allow you to check your work and see how you did. A link will be provided for you at the end of the module.

Exercise 1

M2.E1 a)

  1. If a red eyed albino cat and a black cat that was homozygous for the dilution gene mated what colour would the kittens be?_________________________________________________
  2. Using the mating described in the previous question, what (if any) recessive genes would the kittens carry and what percentage of kittens in the litter would carry them?____________________________________________________
  3. The phenotype of a heterozygous albino(Cc) would be albino True or False? _____________
  4. Does the albino gene mask colour or remove the colour of the cat?_________________________________

 

 

M2.E1 b) Fill in the punnet square below and answer three questions below…

  1.  What percentage of kittens were albino?_________________________________________
  2.  What colour were the kittens which were not albino?_______________________________
  3. What percentage of albino kittens were likely to be male?_______________________________

 

 

 

2.2 Dominant white

Dominant white is the gene most commonly associated with deafness. Unlike the albinism gene which causes the absence of colour in the cat, the dominant white gene masks colour. This means a dominant white cat can still be genetically black, chocolate or any colour you can think of but the dominant white gene will mask it making the cat appear completely white. The dominant white gene is what is known as ‘epistatic’ to all other colours. This means that it will mask even a red or tortoiseshell cat leaving us with a cat that is pure white in appearance or phenotype. Like the dilution gene it is an autosomal trait, meaning that it is not carried on the X chromosome so both male and female cats are affected equally.

Dominant white cats most commonly have either blue eyes, orange eyes or odd coloured eyes. The correct term for odd coloured eyes is ‘heterochromia’. Dominant white cats with blue eyes have a high chance of being either deaf of having hearing issues. Dominant white cats with odd eyes where one eye is blue and the other orange (or any other colour) are likely to be deaf on the blue eyed side while dominant white cats with orange eyes are much less likely to be deaf at all.

The dominant white gene is symbolised by the letter ‘W’. Capital ‘W’ means the cat has the dominant white gene and lower case ‘w’ means the cat does not have the dominant white gene. For a dominant white cat to appear in a litter at least one of its parents must be dominant white. This is because it is a dominant gene and only needs one copy of it to be present in order to show itself in the phenotype of a cat. Only a homozygous recessive cat (ww) would be coloured.

Let’s look at what would happen if we mated a Blue male who did not carry chocolate or cinnamon to a chocolate female who carried dilute had the dominant white gene making her appear white…

Firstly our punnet square with the information of the parents filled in (excluding the dominant white gene) would look like this:

If we fill in the information from both parents into the results boxes excluding the dominant white gene our punnet square will look like this….

You can see from this that 50% of kittens would be black, carrying chocolate and also carrying dilute and 50% of the kittens would be blue carrying chocolate.

Now we shall fill in a punnet square to look at the dominant white gene…

The male is blue so we know his genotype in regards to the dominant white gene is ‘ww’. The female (in this example) has a genotype of ‘Ww’ when concerning only the dominant white gene. When we take into account the dominant white gene we can see that 50% of the kittens would have the dominant white gene and be white in phenotype but would still pass on their hidden colour to their kittens just as it they would if the dominant white gene were not present. It simply masks the colour that is there.

Because we know that the dominant white gene is autosomal we know that each male and female in the litter has an equal chance of being dominant white or not.

2.2A How the dominant white gene affects cats…

i) Sight

We know that dominant white cats can have blue eyes, orange eyes or odd coloured eyes but does the colour have anything to do with eye function? If it does, how can we improve this with genetics?

The dominant white gene affects the embryo during development and causes tapetum lucidum to be absent. Tapetum lucidum is found just below the retina and is a collection of very flat cells which bounce extra light back to the retinal cells and so gives the eyes enhanced visibility during times of low light levels. This means that dominant white cats that have blue eyes often have poorer night vision compared to cat with regular eyes that do have tepetum lucidum present.

Not all dominant white cats with blue eyes experience this however…

The foreign white…

Breeders knew that dominant white cats came with their inherent set of issues which are not something people want to breed in their lines. In the 1960’s it was the idea of a breeder to produce a completely white cat of oriental type and

A beautiful foreign white

style and with gorgeous blue eyes. Patricia Turner was responsible for this breeding program and she crossed seal point Siamese cats with dominant white orange eyed British shorthairs to begin creating the very first foreign white cats that can be found today.

Knowledge of genetics enabled people to use the Siamese gene to give blue eyes yet leave tepetum lucidum in place, preserving the cat’s ability to see perfectly as it should even in low light levels. This type of blue eye where the tepetum lucidum is present are referred to by breeders as Siamese-blue eyes. Eyes that are blue as a result of dominant white and do not have tepetum lucidum are refered to as white-blue eyes.

Most foreign white cats will have Siamese blue eyes though some can still have white-blue eyes and some even have odd eyes; having one with and one without tepetum lucidum. A vet can check what type of eyes an individual cat has with a simple and non-invasive eye exam from the age of 4 months when tepetum lucidum is evident.

During the breeding of the foreign white cats it was discovered that the red gene was not compatible and when breeding red point Siamese to dominant white cats the wardenburg syndrome would often occur. The line was stopped and breeders focused their efforts onto the seal point lines.

ii) Hearing

We discussed how the dominant white gene causes an absence of tepetum lucidum in the eyes and tepetum lucidum is formed from the same stem cells as melanocytes which are responsible for pigment. The cochlea in the ear works by having a ring of melanocytes which regulate the ion balance in the ear. This allows small electrical signals to be passed to the brain via tiny vibrations of the hairs in the ear. To do this the ions need to be constantly regulated. Because dominant white affects the stem cells which produce tepetum lucidem we also see effects on the malanocytes which are as we know, responsible for regulating the ion balance and thus allowing sound transmition. This is why cats are commonly(though not always) deaf of the blue eyed side in the case of odd eyes or both sides in the case of a pair of blue eyes…or rather blue eyes that have not got tepetum lucidum.

All deaf white cats are removed from breeding programs and many leading pedigree cat registration bodies will not permit deaf cats to be registered as breeding cats and any kittens resulting from such a mating will not be eligible for registration in most cases.

Exercise 2

M2.E2 a) What is the correct term for odd eyes?______________________________________

M2.E2 b) Fill in the punnet square below for the following mating: D heterozygous dominant white male who is chocolate carrying cinnamon and a female who is chocolate carrying cinnamon.

  1. What colours would you potentially see in the litter?_________________________________
  2. What percentage of kittens would be white?_________________________________________

 

Exercise 3

M2.E3 Dominant white cats are always deaf: true or false? __________________________

 

2.3 White spotting gene

Finally we shall move on to cover the last gene responsible for causing white to occur in cats. The white spotting gene

A gorgeous blue and white kitten

is a very interesting gene indeed! It is a semi-dominant gene symbolized by the letter ‘S’. It causes cats to be splashed with varying amounts of white.

What is a semi-dominant gene?

semidominant

adjective Referring to the phenotypic effect of a particular allele on another allele with respect to a given trait. Allele A is said to be semidominant with respect to allele a if the A/A homozygote has a mutant phenotype and the A/a heterozygote has a less severe phenotype, while the a/a homozygote is wild-type.

The above description was taken from the free dictionary: Link to the medical dictionary – the free dictionary

From this we can see that in the case of the white spotting gene that the homozygous recessive (ss) results in a normal type or wild type i.e. whatever the cats’ genetic colour happens to be. This could be black, chocolate red or any other colour. For this example we shall say our cat is black. A black cat with the genotype ‘ss’ would result in a

black cat while a black cat with the genotype ‘SS’ or ‘Ss’ would result in a phenotype displaying the mutant gene i.e. the cat would be a black and white cat.

It is noted that cats with a genotype of Ss often have a lesser effect on their phenotype so cats with a lesser amount of white may well be genotype Ss as opposed to a cat that is all white or nearly all white would be more likely to have the genotype SS.

The white spotting gene as we mentioned causes varying degrees of white that will be displayed on the individual cat. These varying amounts of white are split into 10 grades according to how much white is displayed. These 10 grades are in turn split into three main categories: Low  white, Medium white and last but not least high white. The low white category includes grades 1-4, the medium white category includes only grade 5 and the high white category includes grades 6 -10.

Below you can see each of the grades illustrated and grouped into their correct category.

 

When you look at the picture you will notice that the grade 10 white spotting cat is completely white just as would be the case in the dominant white cat. There are two primary ways to tell the difference. One of which is genetic testing. A laboratory specialising in genetics can analyse a DNA collected on an oral swab and let you know if your cat has certain colour traits. This is usually not too expensive and at the time of writing in the UK you would be looking at paying around £40-50 for a single colour test. Most labs offer discount for multiple tests and offer packages. These companies can also provide useful tests to allow you to test for the presence of certain health complaints which could be passed onto kittens.

Another way in which you might be able to get a fairly good idea is by looking at eye colour though this is not entirely reliable since although dominant white cats mostly have blue eyes, orange eyes or odd coloured eyes with one orange and one blue eye there are dominant white cats which have been reported to have green eyes or green orange eye though this is far less common. It can be useful to give you a rough idea though and as a general point of interest.

Exercise 4

M2.E4 If you have a solid white cat in front of you and you do not know what its parentage is – aside from genetic testing and taking into consideration eye colour – can you think of another reliable way that is as reliable as genetic testing in which you would be able to deduce if the cat is a grade 10 white spotting cat or a dominant white cat?________________________________

.

So how does the white spotting gene affect other colours? The answer to this is that it doesn’t really affect them a great deal. The usual colour and pattern of the cat with still be displayed yet it will simply have varying degrees of

A Calico cat clearly illustrating the grouping of colour when combining tortoiseshell and the white spotting gene

white on its body. The only colour that is quite strikingly affected by the white spotting gene is the tortoiseshell. When a tortoiseshell has the white spotting gene present then the brindled effect usually seen in the tortoiseshell will become less brindled and instead the red and black flecks will group together to make larger patches of either red or black giving rise to what is commonly referred to as the calico.

The more white that is present the more the red and black will group and the bigger the patches will become. A cat which is only a grade 2 or 3 white spotting cat may still have a very brindled appearance but a grade 6 or 7 cat will have bold patches of red and black alongside the white. As with the other genes responsible for white in cats, the white spotting gene is not a sex linked trait and both males and females will be affected equally.

Exercise 5

M2.E5 a) Using what you have learned about cat genetics so far can you identify the most likely pair of parents for each of the kittens pictured below? For this exercise we shall assume that none of the parents are carriers and so we are basing our answers purely on the phenotype of the parents. This is to enable you to begin to really get to grips with what colours are recessive and which ones are dominant and to enable you to begin developing and eye for what may show up in a litter even with white thrown into the mix.

Parent couple choices…

 

 

M2.E5 b) Below are pictures of white cats with various coloured eyes. Each pair of eyes belongs to a pure white cat of unknown genotype. Try to answer the questions using the illustration and what you have just learned to help you figure out the answers.

 

  1. Of the cats eyes above which one/s would be highly likely to be deaf on both ears? ______
  2. Of the cats eyes above which cat/s would be highly likely to be deaf on one side?________
  3. Looking at the cats eyes in the picture, how many cats are highly likely to be dominant white cats?_______
  4. How many cats are albino? ____________

 

I hope you have enjoyed this module, it was a bit shorter than the first module because you have already learned much of the basics and we are simply adding to our knowledge. Next module we shall revisit the albino gene to take a look at the Siamese and Burmese variations – a nice short module for you before we dive into the wonderful world of tabbies on module 4! See you next month for module 3 Siamese and Burmese and the genes responsible for them! If you enjoyed this module then jump in the comments below and let us know what you enjoyed…it will help us give you more of the same in the future:-)

If you would like to see the answers to this module please click here!

Resources

Punnet squares PDF Printable Blank punnet squares sheet – help yourself for your own personal use for during this course and for working out your own colour probabilities.

Feline colour genetics course module 2 worksheet – printable PDF

Picture credits

Once again a huge thank you to everyone who kindly donated images for ths module, it was a great help and the module just wouldn’t be the same without your beautiful pictures!

Smirnoff the albino cat https://www.flickr.com/photos/29987430@N05/

Foreign white with special thanks to Ross of siamese-cat-breeder.co.uk

Blue and white kitten – special thanks to a member of the furkidz.org family.

All other photographic images were from free sources.