Basic Notes on Cat Genetics

SOME VERY BASIC COAT COLOUR GENETICS

GENOTYPE refers to the genetic makeup of a cat for example a cat may be said to be black carrying chocolate and blue

PHENOTYPE refers only to what you see for example a black cat

WHAT ARE GENES?
Domestic cats have 19 pairs of chromosomes
They receive a chromosome from each parent
Each chromosome contains many thousands of genes
The genes on each chromosome are at the same location
The copy of the gene on each chromosome can be different and each copy is referred to as an Allele
There may be more than two possible versions or alleles of each gene for example there are three different tabby genes, blotched, mackerel and ticked.

AUTOSOMAL AND SEX GENES
Genes fall into 2 categories

Sex Linked Genes are those located on the XX and XY chromosomes
Traits on these genes are said to be sex linked for example the red gene in cats is on the X chromosome therefore a female cat can carry a trait with one copy of the gene whereas the male with one copy will show the trait, a male with an X sex linked trait can only pass that trait onto his daughters, his male kittens must receive a Y chromosome from him in order to be male, a classic example is the red gene.

Autosomal Genes are the genes located on any chromosomes other than the sex chromosomes XX and XY

GENE EXPRESSION
Dominant (represented by an upper case letter) for example the agouti gene if the cat has one dominant allele they will show tabby markings
Recessive (represented by a lower case letter) for example a cat must have two copies of the recessive chocolate gene to have a chocolate coat
Incompletely Dominant where both genes have some expression for example if a cat receives a pointing gene and a sepia gene they will have a mink coat pattern
Epistatic where the gene suppresses the expression of another gene for example the dominant white gene hides the expression of all other coat patterns and colours.
Polygenic where groups of genes work together to produce certain characteristics.

THE BASIC GENES FOR CAT COAT COLOUR
The alleles for the coat colour genes are represented by B for Black or b for Chocolate. The alleles for coat colour density genes are represented by D for dark (dense Black or Chocolate) and d for dilute (Blue or Lilac)

SOME EXAMPLES OF DOMINANT & RECESSIVE TRAITS, (GENES) AND SYMBOLS

Dominant Traits
Always represented by a
capital letter
Possible Genotypes Recessive Traits
Always represented by a
lower case letter
Possible Genotype
White Spotting S S or Ss No White Spotting s ss
Agouti
A Tabby
A or Aa Non Agouti a
Non Tabby
aa
Dense Coat Colour D
Black or Chocolate
D or Dd Dilute Coat Density
Blue or Lilac
dd
Melanin Inhibitor I
Silver or Smoke I
I or Ii Non Silver i ii
Full Coat Colour C Ccs, Ccb, Cca, Cc Albino Alleles - cs cb ca c
For further explanation see Albino Alleles
Pointed Cats may be
cs cs or cs cb or cs cc
Sepia Cats may be
cbcb or cbcs or cb ca or cb c
Mink cats are
cbcs
Blue eyed White cats may be
caca or cac
red eyed white cats would be
cc
Short Hair L L or Ll Long Hair l ll
Manx M
Semi Lethal MM kittens die in utero
M or Mm Non Manx m mm

Any of these recessive Traits can 'hide' and show up out of the blue. However when you are breeding cats, or know some of their history you can often figure out what they are carrying in the way of recessive genes.

If a cat showing any recessive trait is mated, all of their progeny will either show the recessive trait or carry a copy of it.

Two cats showing a recessive trait, when mated to one another cannot produce kittens showing the dominant expression of that trait, for example two long haired cats cannot produce a short haired kitten.

With the dominant allele of any gene at least one parent must show it for any progeny to show it, for example a Tabby crossed with a non Tabby may produce Tabbies, however two Non Tabbies cannot produce any Tabby kittens.

RED & DOMINANT WHITE

These two genes are unusual, in that their presence is able to mask or 'paint over' other colours, this is referred to as EPISTASIS.

Dominant White symbol W

Because of this paint over effect, every Red or Cream or Pure White cat is actually another colour underneath. A pure white cat may be any colour or coat pattern under the White, including Red and Cream, Pointed, Sepia, Mink, Tabby etc

Dominant white is totally different from White Spotting. White Spotting is the typical cat with anything from a white bib right through to just a few spots of colour on an otherwise white cat.

Red symbol Xo (Sex Linked)

Red cats are actually either Black or Chocolate while Cream cats are either Blue or Lilac. Unlike Dominant White the Red gene does not cover coat pattern, e.g. PointingSepia, Mink and Bicolour can all show through the red In other words, the cat actually has the genes for these colours but they are unable to be expressed (show).

Red also affectsthe Agouti (Tabby) genes, in that it allows the tabby pattern to show even on cats that are in actual fact Non Tabby.

The Red gene is sex linked, it only occurs on the X chromosome, not the Y chromosome. Therefore if a male cat (XY) receives an X chromosome from his Mother with the Red gene on it, he will be red or cream.

Because a female has two X chromosomes (XX) they may receive either one or two X chromosomes containing the Red gene. If they receive one red X, they will be Tortoiseshell, if they receive two red X chromosomes they will be red or cream. The tortoiseshell coat pattern is caused by the fact that in female cats one of the X chromosomes in each cell is turned off while the other is left turned on (this is to help even things up, as the Y chromosome of the male is smaller with less room for genetic information. So a tortoiseshell female will show red or cream coat in some areas and there underneath coat colour in others depending on which X chromosomes are turned off and which are turned on!

Tortoiseshell males only occur in male cats who have abnormal chromosomes, e.g.. XXY

See the mating chart below

TABLE OF RED CAT MATINGS

Mating
Red
Males
Non Red
Males
Red
Females
Tortoiseshell
Females
Non Red
Females
Red Male x Non Red Female No Yes No Yes No
Red Male x Tortoiseshell Female Yes Yes Yes Yes No
Red Male x Red Female Yes No Yes No No
Non Red Male x Tortoiseshell Female Yes Yes No Yes Yes
Non Red Male x Red Female Yes No No Yes No
Non Red Male x Non Red Female No Yes No No Yes

WHITE SPOTTING (S) GENE

White Spotting as just mentioned is the gene responsible for your typical bicolour cat.

The White Spotting gene is dominant. This gene has what we call Variable Expression, as you can see from the many varied Bicolour patterns you see in the cat population, from mere smudges of white, through to all white with smudges of colour

When a cat has both White Spotting genes i.e. SS, they will have a greater proportion of white than those with only one of the genes i.e. Ss.

The White Spotting gene also affects other genes. Tortoiseshell cats with white on their bodies will have large patches of colour, as opposed to those without any white where the colours are all mixed.

White Spotting also affect the Pointing and Sepia genes. Again when there is white on the body of the cat, the coloured parts of the body will often become almost as dark as the mask and tail.

AGOUTI GENE (A) ALLOWS TABBY COAT PATTERN
TO BE EXPRESSED (TO SHOW)

Firstly you need to know that all cats have genes for what tabby pattern they would or will have if they inherit the dominant Agouti gene. There is still debate regarding tabby genetics in cats. There are three possible tabby alleles, in order from dominant through to recessive these are Ticked (Ta), Mackerel (Mc), Classic (mc). There are theories that the ticked tabby pattern masks the other two tabby patterns. It is now thought that a modifying gene or genes referred to as the Spotting gene (SP) breaks up the non ticked tabby patterns to produce spotted tabbies. It will be interesting to follow the ongoing research into tabby cats.

As mentioned under the red gene, if the red gene is present it allows the tabby pattern to show even in a non agouti cat.

Some high grade smoke cats may also show a ghost tabby pattern, especially while they are young.

THE ALBINO COAT COLOUR IN CATS

Albino Genes Responsible For Pointing, Burmese (Sepia)
and Tonkinese (Mink) Coat Patterns

This set of alleles are interesting in that their expression is affected by body temperature, making cooler body parts grow darker hair which explains why the resulting coat patterns are darker on the legs, ears, face and tails and lighter in the main warmer body of the cat.

Burmese also known as Sepia and Tonkinese also known as Mink are terms which refer both to a particular breed of cat and to a particular coat pattern in any breed of cats. Whereas Pointing is used to describe the coat pattern seen in the Siamese, Birman etc. Kittens born with these coat patterns, are born white through to a light coffee colour and develop their colours slowly over the first months of life. The first photo shows Oscar at 2 days coffee coloured kitten in foreground, the second at 10 weeks. The last photo shows Oscar in foreground still growing an adult coat, Monica in background is the same colour but with her adult coat!

DevonRex Stud Cat Ocsar at 2 days oldDevonRex Stud Cat Ocsar at 2 days oldDevonRex Stud Cat Ocsar at 2 days old

You Can Also Check Out Wisecracks Cilla Consealer changing
from her newborn colourless state to her adult colouring here

The Dominant form of this gene is C or full coat colour

The Albino Alleles in order from dominant through to recessive are

Full Coat Colour, symbol C
Pointing, symbol cs
Burmese, symbol cb
Blue eyed White symbol ca
Red eyed white symbol c
Because cb or or cs are of 'equal power when a cat has a copy of each the genes share expression these cats are Tonkinese (Mink cb cs )

The Pointing and Sepia genes change Black to Seal, other colours remain unchanged. Pointing and Sepia genes are affected by the White Spotting gene (see White Spotting)

SILVERS TABBIES & SMOKE

Action of the Inhibitor Gene symbol I

The Inhibitor gene is responsible for Smoke and Silver Tabbies. The gene literally inhibits the formation of colour at the base of the hair. The higher the grade (or expression) of this gene the further up the hair shaft the colour is inhibited. A tabby cat with this gene is referred to as a Silver Tabby, the most extreme of the expression being seen in the Chinchilla coat, these cats are actually very high grade Black Silver Tabbies. A non tabby cat with the same gene will be referred to as a Smoke.

The Inhibitor gene in Devons can actually change the colour of the cat significantly as they move from their juvenile suede coat to their adult coat. When they are sporting their suede coat the kittens or young cats may almost look pointed, with the shortest of their coats being very light, while their face, legs ears and tail are their adult darker colour.

TABLE OF RED CAT MATINGS

Mating
Black Blue Chocolate Lilac Kitten Carry
Blue x Blue
B-dd x B-dd
No Yes No If both parents carry chocolate
Blue x Chocolate
B-dd x bbD-
Yes If chocolate parent carries dilute If blue parent carries chocolate If chocolate parent carries dilute and blue parent carries chocolate All kitten will carry blue
Blue x Black
B-bb x B-D-
Yes If black parent carries dilute If both parents carry chocolate If black parents carries dilute and chocolate and blue parent carries chocolate All kittens carry blue
Blue x Lilac
B-dd x bbdd
No Yes If blue parent carries chocolate If blue parent carries chocolate All kittens carry blue & chocolate
Black x Chocolate
B-D- x bbD-
Yes If both parents carry dilute If black parent carries chocolate If black parent carries chocolate and blue and chocolate parent carries dilute All kittens carry chocolate
Black x Black
B-D- x B-D-
Yes If both parents carry dilute If both parents carry chocolate If both parents carry dilute and chocolate
Black x Lilac
B-D- x bbdd
Yes If black parents carries dilute If black parent carries chocolate If black parent carries dilute and chocolate All kittens carry dilute and chocolate
Chocolate x Chocolate
bbD- x bbD-
No No Yes If both parents carry dilute All kittens carry chocolate
Chocolate x Lilac
bbD- x bbdd
No If chocolate parent carries dilute Yes If chocolate parent carries dilute All kittens carry chocolate and dilute
Lilac x Lilac
bbdd x bbdd
No No No Yes
all kittens will be Lilac
All kittens carry chocolate and dilute

- indicates carried allele unknown

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