Feline Genetic Loci Table

Last Updated on November 30, 2021 by Julia Wilson

Coat colour

B – Brown Locus

B/BHomozygous – Black/BrownBlack/Brown
B/bHeterozygous – Black/Brown – carries ChocolateBlack
B/blHeterozygous – Black/Brown – carries CinnamonBlack
b/bHomozygous – ChocolateChocolate
bl/blHomozygous – CinnamonCinnamon – reddish chocolate
b/blHeterozygous – Chocolate – carries CinnamonChocolate
The Chocolate allele whilst recessive to the Black allele is dominant to cinnamon. Thus a chocolate cat can carry the cinnamon allele, a Black cat can carry either chocolate or cinnamon and a cinnamon cat can only be homozygous cinnamon.
ba – Barrington Brown Locus (example only)
Ba/BaHomozygous – Non-Barrington BrownCat unaffected – ie Black/Brown/Chocolate etc
Ba/baHeterozygous – Non-Barrington Brown – carries Barrington BrownCat unaffected – ie Black/Brown/Chocolate etc
ba/baHomozygous – Barrington Brown -liberty of renamingMahogany Brown/Light Brown/milk coffee in colour

I took the liberty of renaming Shaw’s Barrington Brown allele so that it could be used as an example of a recessive brown locus in this table. The Barrington brown cats were b/b/, ba/ba – the two alleles had an additive effect on each other and created the pale milk coffee coloured cats. It has only been added as an example as the colony of cats were never seen outside the laboratory nor did any of the cats leave the laboratory. But it is an example of a further recessive brown locus.

O – Red Locus

XO/XOHomozygous – Red FemaleRed Series female
XO/XoHeterozygous – Tortishell femaleFemale Red Series intermingled with other base colour i.e.. Black tortie, chocolate tortie
Xo/XoHomozygous – Non-red femaleno effect – no red or tortoiseshell
XO/YRed MaleRed Series male
XoYNon-red maleNo effect – no red
XXY & similarMosaicRed series intermingled with base colour – i.e. Black tortie (unusual)

Sex-linked to the X chromosome. Cream is the dilution of red and thus also sex-linked and Apricot is the Dilute modifier variations of cream and thus also sex-linked. E.g.. d/d, dm/dm, XO/XO = cream; d/d, Dm/-, XO/XO = Apricot

C – Colouration Locus
C/CHomozygous – Solid ColouredCat solid colour
C/cHeterozygous – Solid Coloured carrying red-eyed albinoCat solid colour
C/caHeterozygous -Solid Coloured carrying blue-eyed albinoCat solid colour
C/csHeterozygous – Solid Coloured carrying colour pointCat solid colour
C/cbHeterozygous – Solid Coloured carrying sepiaCat solid colour
c/cHomozygous – Pink eyed Albino (recessive white)No Pigment (Albino) White cat with Pink eyes
ca/caHomozygous – Blue-eyed Albino (recessive white)No Pigment (Albino) White cat with pale blue eyes
cs/csHomozygous – Colour PointPointing/Siamese – high-grade point definition
cb/cbHomozygous- SepiaSepia/Burmese- low-grade point definition
cb/csHeterozygous- Mink – Sepia & Point (co-dominant)Mink/Tonkinese – mid-range point definition
cs/caHeterozygous – BondanesePointing/Siamese – high-grade point definition, with a paler coat
cb/ca* – heterozygous- Sepia & Blue-eyed albinoNot enough information to determine the phenotype
cs/c* – heterozygous Point & Red-eyed albinoNot enough information to determine the phenotype
cb/c* – heterozygous Sepia & Red-eyed albinoNot enough information to determine the phenotype
ca/c* – heterozygous Blue-eyed albino & Red-eyed AlbinoNo Pigment (Albino) White cat with pale blue eyes
*The combinations above have been given no names. The gametes cb and cs are co-dominant to each other and create mid-range point definition known as a mink cb/cs. There is little data on the gametes ca, c and their effects on cb and cs.
D – Colour Density Locus
D/DHomozygous – Dense – Darker pigmentationCat dark colour, e.g., black, chocolate, cinnamon, red etc.
D/dHeterozygous – Dense – carrier of dilutionCat dark colour, e.g., black, chocolate, cinnamon, red etc.
d/dHeterozygous – DiluteDilutes colours – e.g. blue: B/-,DD, lilac: b/b, d/d, cinnamon: bl/bl,d/d
Dense and Dilute colours: Black (B/-,D-) = Blue (B/-,d/d); Chocolate (b/b, D/-) = Lilac (b/b, d/d); Cinnamon (bl/bl, D/-) = Fawn (bl/bl, d/d); Red (XO/XO, D/-) = cream (XO/XO, d/d)at
Dm – Dilute Modifier Locus
Dm/DmHomozygous – Dilute ModifierModifies Dilutes – caramel tone
Dm/dmHeterozygous – Dilute Modifier – carrier of non-dilute modifierModifies Dilutes – caramel tone
dm/dmHomozygous – Non-dilute ModifierNo effect
The Dilute Modifier only affects dilute colours. It has no effect on Dense colours. Thus for the phenotype to be affected by the Dilute modifier the cat needs the genotype (d/d, Dm/-). A cat that is (D/d, Dm/-) may possess the Dilute modifier allele but the coat is unaffected because the Dm allele only affects dilutes.
S – White Piebald Spotting Locus
SSHomozygous – White Piebald spottedMedium to high levels of white spotting
S/sHeterozygous – White-spotted carries non-spottingLow to medium levels of white spotting
s/sHomozygous – Non-White Piebald-spotting.No white spotting, solid coloured cat.
The Piebald allele displays variable expression – control of this expression is as yet undetermined. However, generally, cats with high-grade white markings, such as harlequin and Vans, tend to be homozygous Piebald.
W – White Locus
W/WHomozygous – WhiteAll white coat masking cats colour
W/wHeterozygous – White – carrying non-whiteAll white coat masking cats colour
w/wHomozygous – Non-whiteNo effect – no white
The white allele can also cause a developmental cascade of events where open the melanocytes fail to migrate over they eyes (resulting in blue eyes or one blue eye) and/or cause degenerative changes to occur in the saccule and cochlea caused by lack of migration or viable migration (resulting in partial or total hearing loss).

Agouti Variations & Inhibitors- Tabby patterns & Smoke/Silvers

A – Agouti Locus
A/AHomozygous – AgoutiAgouti banding of the hair shaft
A/aHeterozygous – Agouti – carries non-agoutiAgouti banding of the hair shaft
a/aHomozygous – Non-AgoutiNo banding of the hair shaft
This allele determines the phenotypic absence or presence of the Tabby alleles. The variation in Agouti banding is determined by the Tabby Allele Series – see below
Mc/mc – Mackerel Tabby/Classic Tabby Locus
Mc/McHomozygous – Mackerel TabbyMackerel Tabby
Mc/mcHeterozygous- Mackerel – carrying Classic TabbyMackerel Tabby
mc/mcHomozygous – Classic TabbyClassic Tabby Markings on coat
Both Mackerel and Classic tabbies are modified by ticked tabby allele and the spotted tabby allele. They must have non-ticked (ta/ta) and non-spotted (sp/sp) alleles present in order to allow the Mackerel/Classic tabby allele to display its phenotype, e.g.: ta/ta sp/sp, Mc/mc = mackerel tabby carrying classic tabby allele (with no ticking or spotting). See Ticked tabby Locus for another eg.
Sp – Spotted Tabby Locus
Sp/SpHomozygous – Spotted TabbySpotted Tabby
Sp/spHeterozygous – Spotted Tabby – carrying non-spottedSpotted Tabby
sp/spHomozygous – Non-Spotted TabbyNo effect
The Spotted Tabby allele is a dominate modifier of both the mackerel and classic tabby allele but is recessive to the ticked tabby modifier allele. e.g. ta/ta, SP/sp, Mc/mc = Spotted tabby carrying non-spotting allele, masking the mackerel tabby allele carrying the classic tabby allele (with no ticking)
Ta – Ticked Tabby Locus
Ta/TaHomozygous – Ticked TabbyTicked Tabby
Ta/taHeterozygous – Ticked TabbyTicked Tabby
ta/taHomozygous – Non-Ticked TabbyNo Effect
Ticked tabby allele is a dominant modifier to all other Agouti variations. The cat must have ta/ta to see the other variations. E.g., TA/ta, SP/sp, Mc/mc = is a ticked tabby carrying non-ticked tabby and masking Spotting, carrying non-spotting and masking the Mackerel tabby allele that carries the classic tabby allele. See above for more examples.
I – Inhibitor Locus
I/IHomozygous – Inhibitor – SilverSmoke/silver tabby/tipped/shaded – base to mid – to upper hair shaft white
I/iHeterozygous – Inhibitor – carrier of non-inhibitorSmoke/silver tabby/tipped/shaded – base to mid – to upper hair shaft white
i/iHomozygous – Non-InhibitorNo effect
The inhibitor allele has variable expressions in combination with the agouti and non-agouti alleles and variable banding on the hair shaft. Smokes are the non-agouti inhibitor combination and of course, the silver tabbies are the agouti-inhibitor combination. Chinchilla/shaded/tipped are also inhibitor agouti combination but with the addition of wide banding on the hair shaft. The Inhibitor allele can combine with all agouti variations (Silver tabby series)

Coat texture and length

L – Hair Length Locus
L/LHomozygous – ShorthairShorthair
L/lHeterozygous – Shorthair – carries long hairShorthair
l/lHomozygous – longhairLonghair
The longhair allele displays variations in length- for semi longhair of the Turkish Angora, to the longhair of the Persian (phenotypically different coats but the alleles that control the hair length are the same). The shorthair allele also is variable, from the short coat of the Siamese to the short coat of the Exotic shorthair (phenotypically different coats but the alleles that control them are the same)
ls – Recessive Shorthair (no gene code has been allocated – this is only being used as an examples)
Ls/LsHomozygous – LonghairLonghair
Ls/lsHeterozygous – Longhair – carries short hairLonghair
ls/lsHomozygous – ShorthairShorthair
This is a (rare) autosomal recessive shorthair to Longhair and has been found in some Persians lines. Shorthaired kittens are produced from longhaired cats.
r – Cornish Rexing Locus
R/RHomozygous – Straight haired catStandard coat – no effect
R/rHeterozygous – Straight haired cat carries – C rexingStandard coat – no effect
r/rHomozygous – C rexed catRexed – wavy fur
The curly coat resulting from the Cornish rex allele is recessive to normal coats but is co-dominate to the Devon Rexing allele. A cross between a Devon and a Cornish Rex results in a straight coated cat because they are on two different Loci. First cross would get R/r Re/r. But a further cross between offspring could result in 1/16 r/r re/re – a cat that is both a Cornish rex and a Devon rex.
re – Devon Rexing Locus
Re/ReHomozygous – Straight haired catStandard coat – no effect
Re/reHeterozygous – Straight haired cat carries – D rexingStandard coat – no effect
re/reHomozygous – D rexed catRexed – wavy fur
The curly coat resulting from the Devon Rex allele is recessive to normal coats but is co-dominate to the Cornish Rexing allele. See above.. The Devon Rex allele is however recessive to the Sphynx allele.
ro – Oregon Rexing Locus
Ro/RoHomozygous – Straight haired catStandard coat – no effect
Ro/roHeterozygous – Straight haired cat carries – O rexingStandard coat – no effect
ro/roHomozygous – O rexed catRexed – wavy fur
The curly coat resulting from the Oregon Rex allele is recessive to normal coat and on a different locus to both the Cornish and Devon rexing allele a cross between the Oregon Rex and either the Cornish or Devon rex results in a cat with a straight coat, this cat is no longer bred.
Se – Selkirk Rexing curl Locus
Se/SeHomozygous – S Rex catRexed – wavy fur
Se/seHeterozygous – S Rexed cat – carrying a normal coatRexed – wavy fur
se/seHomozygous – Straight haired catStandard coat – no effect
The curly coat resulting from the Selkirk allele is a dominant trait and thus can carry straight The homozygous Selkirk has a finer, curlier and sparser coat than the heterozygous Selkirk. Thus all show Selkirks are heterozygous. S
Lp – Laperm Rexing Locos – (I can find no gene code allocated – this is only being used as examples)
LP/LPHomozygous – LP Rex catRexed – wavy fur
LP/lpHeterozygous – LP Rexed cat – carrying a normal coatRexed – wavy fur
lp/lpHomozygous – Straight haired catStandard coat – no effect
I was unable to find the gene code (so I took liberties in using Lp – if I find the correct code this will be adjusted) But the mode of inheritance will not change and it is a good example of dominant rexing. Their coat can be wavy or have lots of ringlets.
wh – Wire Hair Locus
Wh/WhHomozygous – WirehairBristly, wiry fur
Wh/whHeterozygous – Wirehair carries – straight hairBristly, wiry fur
wh/whHomozygous – Straight hairStandard coat – no effect
The wiry coat resulting from the Wirehair allele is a dominant trait and thus the cat can carry normal hair. The Wire Hair allele has incomplete penetrance – thus cats with the dominant allele may have a normal coat – but produce cats with the wiry coat.
hr – Hairless Locus – Canadian Hairless – Sphynx cat
Hr/HrHomozygous – Coated catStandard coat
Hr/hrHeterozygous – Coated cat – carries Sphynx hairless alleleStandard coat
hr/hrHomozygous – Sphynx Hairless cathairless cat
The Sphynx allele is a receive allele and only homozygous Sphynx can be hairless. It can be carried by normal coated cats from outcross programs. They Sphynx allele is dominant to the Devon Rex allele. The French Hairless (h/h) and the UK Hairless (hd/HD – extinct) are also recessive hairless alleles – whether they are different or the same allele is uncertain and will never be known as both the UK and French Hairless are extinct.
Hp- Peterbald/Don-Sphynx Locus – (I can find no gene code allocated – this is only being used as an example)
Hp/HpHomozygous – Hairless Peterbald/Don-SphynxHairless cat
Hp/hpHeterozygous – Hairless -carrying a normal coatHairless cat
hp/hpHomozygous – Coated catStandard coat – no effect
I was unable to find the gene code (so I took liberties in using Hp – if I find the correct code this will be adjusted) But the mode of inheritance will not change and it is a good example of a dominant trait. Baldness first appears on the head and neck and sometimes cats have a rex coat up to 1-2 years of age.

Ears, tails and toes

Cu – Curled Ears Locus
Cu/CuHomozygous – Curled earsEars Curl backwards
Cu/cuHeterozygous – Curled Ears – carries normal earsEars Curl backwards
cu/cuHomozygous – Normal earsStandard ears – no effect
The curled ear allele is a dominant trait that shows some variability in the degree at which the ears are curled backwards. The curled ears cats appear to have normal ears for the first 12-16 weeks and then they begin to curl backwards. Cats that are heterozygous can produce a normal eared cat.
Fd – Folded Ears Locus
Fd/FdHomozygous – Folded EarsEars Folded Forwards
Fd/fdHeterozygous – Folded Ears – carrying non-folded ears or standard ears (rare)Ears Folded Forwards
fd/fdHomozygous – Normal earsStandard Ears – no effect
The Folded ear allele is a dominant trait with incomplete penetrance. Homozygous folds may have cartilage defects that is rarely seen in the non-folds. Thus breeders breed heterozygous folds to non-folds. Unfortunately, as the allele has incomplete penetrance an occasional normal eared cat from the breeding program may, in fact, be a heterozygous fold. Which can produce breeding problems when the normal eared offspring are used.
M – Manx tail Locus
M/MHomozygous – TaillessRumpy or stump – Homozygous Lethal?
M/mHeterozygous – Tailless – carrying normal tailRumpy or stump tail
m/mHomozygous – Normal tailStandard tail – no effect
The Manx allele is a dominant trait with variable expression from a complete lack of tail (Rumpy) to a foreshortened tail (stumpy). The allele has been referred to as a prenatal homozygous lethal (meaning M/M cats die in the womb) – but this is being questioned by Manx breeders. The Manx allele has been associated with several spinal cord anomalies.
Pd – Polydactyl Locus
Pd/PdHomozygous – PolydactylExtra toes
Pd/pdHeterozygous – Polydactyl – carrying normal N# toesExtra toes
pd/pdHomozygous – Normal number of toesStandard number of toes – no effect
The main polydactyl cat trait seen is dominant in action with variable expression – effects ranging from enlargement of the inside digit, to extra toes on each foot or only the front feet. There may be other Polydactyls that appear in different gene populations that are inherited differently.
JP Japanese Bob Tail Locus
JP/JPHomozygous – BobtailShort bobtail
JP/jpHeterozygous – Bobtail tail carrying normal tailShort tail
jp/jpHomozygous- Non-Japanese BobtailNormal tail
The Japanese bobtail is thought to be a dominant trait with incomplete penetrance. Heterozygotes can have a short tail but fail to get the tail folding. This trait is thought to only occur in the homozygous bobtail.
Ad – Achondroplastic Dwarfism (I can find no gene code allocated – this is only being used as an example)
Ad/AdHomozygous – DwarfDwarf – i.e. Munchkin
Ad/adHeterozygous – DwarfDwarf – i.e. Munchkin
ad/adHomozygous – Normal-sized catCat normal size – no effect
Dwarfism is thought to be caused by an autosomal dominant trait. But there are questions as it may be a heterozygous lethal.

Written by Tonia Marsh.