“… originally know as Piebald. The Hooded locus is responsible for many of the different marking variations we commonly see in rats including Berkshire, Irish, Variegated, Essex and Notched as well an Extreme allele….”

The H Locus

Named after one of the oldest and most popular white spotting mutations, the Hooded gene was originally know as Piebald. The Hooded locus is responsible for many of the different marking variations we commonly see in rats including Berkshire, Irish, Variegated, Essex and Notched as well an Extreme allele.

The Hooded allele is recessive, and when the base mutation hh is present the Hooded pattern is produced. HH produces the solid colored wild typing, Self. And Hh produces Berkshire rats that sport a white chest and belly or Irish (not to be confused with English Irish) where the white marking does not extend to the chest, sides or legs.

But the Hooded locus as stated has far more allelic mutations. Essex rats are represented with H^ro and is a lethal dominant gene having gradual color loss from the spine down, fading into an off-white belly as well as head spotting. English Irish is a separate allelic mutation unlike normal Irish, and is recessive being represented as h^i. This variant of Irish only has a chest marking along with some slight white on the feet and tail tip.

There are two more allelic mutations on the Hooded locus that have heavy white marking covering most of the body. Notched rats are marked up to the head with a head spot between the ears that is attached to the white markings of the body giving it its name. The genetic symbol is h^n and it is a recessive mutation. The second of these is the Extreme allele, represented as h^e. This recessive mutation causes the most white marking of any of the other alleles on the locus. It is responsible for Patched, Masked and even Black-Eyed Whites, all sharing the same recessive genome.

Patched rats are mostly white with small patching of coloring in one or a few locations. The patch is often on the head. The Masked marking is likewise a patch of coloring on a fully marked rat, this time being singular and over the upper facial area generally including one if not both eyes. Bareback and Capped are two other varieties that are either h^n or h^e generally. Bareback rats are the same as Hooded but without the dorsal stripe. Capped being limited to the color solely to the head not going past the back of the ears, where even the throat has white markings.

The Extreme allele has also been breed to be completely white, one of the true Black-Eyed White variants. The markings should cover the entire rat with no signs of coloring in the fur. From what I understand this genealogy is not related to megacolon, unlike DWS which is a completely separate locus also responsible for high white markings. Deafness and even epilepsy are sadly an issue in most extremely marked rats however due to markings stunted development also effecting the ears development, and they are even banned from show in the UK.

Two more phenotype come from the Hooded locus that we know of, Variegated and Variegated Berkshire (Variberk). This patterning itself does not have a specific allele but is instead created by a combination of the other alleles on the locus, usually h^ih^e or h^ih^n. It seems to basically take one heavy white spotting gene (such as h^e or h^n) and in combination with the Irish allele, or possibly other genes that adds or preserves color instead of removing it as well creating an uneven splotched pattern or edges to the existing patterns such as Berkshire. There has been ample study of the variegated patterning but there is still many things that are not understood about it’s genetics.

There is however one more allele I’m aware of on the Hooded locus known as the Restricted allele. It is both homozygous lethal and causes sterility in males shortly after puberty. This mutation is not generally breed due to it’s health issues. It also seems to be similar to the restricted allele in it’s effects.

Origins

The Piebald mutation as it was first known is one of the oldest mutations, along with the Black and Albino genes. The Piebald name is derived from the human analog mutation. The first recorded studies including the Hooded mutation where from 1877-1885 by a man by the name of Crampe, though this was pre-Mendelian era.

Cross-Genetics

These mutations are seen in all varieties of rats quite often, but they do have some more specific crosses with other marking genes that seem to gain from certain mutations. This section of the article will be updated shortly with some genetic modifiers and other mutations that or often used in combination with the h locus to create more interesting markings.

 

 

 

RB Mismarked English Irish

Sablinova FRB3, 48 Days Old

 

 

 

 

RB Variegated

Sablinova FRB2, 48 Days Old

 

 

 

 

RB VariBerk

Sablinova FRB1, 48 Days Old

 

 

     STANDARDs

     AFRMA [US] 

HOODED – Hooded rats may be shown in any recognized color. The sides, legs, and feet should be a pure clean white, free from spots or brindling. The hood should cover the head, neck, and shoulders without a break, showing no white on the throat or chin, and should run in an even line around the body. The spine marking should extend in an unbroken line from the hood to the tail, be of moderate width, and be free of ragged edges or brindling. The tail should be colored at the base, then white to the end.

BERKSHIRE – Berkshire rats may be shown in any recognized color. The top color is to be judged as to the recognized color. Distinctive markings are the colored top with a completely white belly and white feet and tail, with a small white spot between the ears. There should be an even line between the top and bottom color. The white markings should be a pure clean white.

IRISH – Irish rats may be shown in any recognized color. The top color is to be judged as to the respective color. Distinctive markings are the white underside, with four white feet and a white tail tip. The under marking should be a pure clean white, of moderate size and as even in shape as possible, not extending onto the legs, sides, or chest. The white feet should resemble the stops on a Dutch rabbit. The tail should be colored for most of its length, with a white tip of no more than one-fourth of its total length.

ENGLISH IRISH – White equilateral triangle on chest with front feet white and back feet white to half their length. The triangle on chest to be of good size, clear and devoid of brindling, not to extend in a streak down the belly but occupying all the space between the front legs. The body color shall conform to a recognized color. (English, N.F.R.S.)

ESSEX – To be recognized in any standard color, remembering that the effect of the gene responsible is to lighten the top color. The darkest area is along the spine, becoming less intense down the sides of the animal. The gradual fading of color continues onto the belly which is off white, with no spotting of darker color. When viewed from above, the fading effect should be symmetrical, having no clear demarcation. The fading effect also to be seen on the legs so that the feet are also off white. There should be no obvious patches of contrasting color. Pied tails not to be penalized. A head spot is essential; this must be well defined, centrally placed on the forehead and symmetrical.

MASKED – Masked rats may be shown in any recognized color. The body is to be a pure, clean white, free from spots or brindling. A colored mask to cover the face, to include just around the eyes and above the nose, not to extend down the sides of the face onto the jowls or under the chin. (Leah Soverns/The Rat Room)

BAREBACK – Bareback rats may be shown in any recognized color and will have markings like the Hooded rat but without a spine marking. The back, sides, legs, and feet should be a pure, clean white, free from spots or brindling. The hood should cover the head, neck, and shoulders without a break, showing no white on top of head, throat, or chin, and should run in an even line around the body. (Karla Barber/Emerald Hill)

CAPPED – Capped rats may be shown in any recognized color. The body should be a pure clean white, free from spots or brindling, with a colored head. The color should be confined to the head area only, not appearing on the throat area. The cap should be free of ragged edges or brindling, follow the line of the lower jawbone in an even line and not extend past the ears.

VARIEGATED – Variegated rats to be shown in any recognized color and are similar to Hooded rats but instead of a spine marking, will have patches and flecks of color on the back side. The head and shoulders to be solid like those of a Hooded rat with a white spot/star on the forehead which should be centrally placed, round or oval in shape, and no bigger than the rat’s eye. The variegation (patches and flecks of color) to evenly cover the rest of the white body from the shoulders to the tail including the sides and tail. Underside (including belly, chest, and throat) to be white, devoid of creamy tinge or staining. (Rev. August 19, 2006)

BLACK-EYED WHITE – To be as white as possible, devoid of creamy tinge or staining. Any colored hairs to be severely penalized. Eyes black. (English, N.F.R.S.) (added July 26, 1987)

BLAZE – Blazed rats may be shown only in Berkshire or Variegated classes in any recognized color. A wedge shaped blaze of white should run from muzzle to ears including the whisker beds, tapering to a fine point at the ears. Other markings as for respective pattern.”

     RMCA [US] 

HOODED – Hooded rats can be exhibited in any recognized color. The hood should be complete, covering the head, throat, chest, and shoulders, except in light colored markings where a pale colored throat and chest is allowable. The hood should be continuous with the spine marking extending down the back to the tail, with as much of the tail as possible being colored. The spine marking should be 1/4 to 1 inch wide, be unbroken, and be as straight and even as possible. All white areas should be free of spots or brindling.

BERKSHIRE – To be symmetrically marked, with as much white on the chest and belly as possible. The white will not extend up the sides of the body, the edges will be clear cut and devoid of brindling. Back feet to be white to the ankle, forelegs to be white to half the leg. Tail to be white to half its length. The body color will conform to a recognized color. The white area will be pure and devoid of any color or staining. A white spot on the forehead or Blaze is desirable.

IRISH – White (inverted) equilateral triangle on chest with front feet white to half their length. The triangle to be of good size, clear cut and devoid of brindling, not to extend in a streak down the belly, but to occupy all of the space between the front legs. The body color to conform to a recognized color.

MASKED – Masked rats can be exhibited in any recognized color. A colored mask should cover the face just around the eyes and above the nose and should not extend down the sides of the face, under the chin, or up to the ears. The rest of the body should be a clean white with no spots or brindling.

BAREBACK – Barebacks can be exhibited in any recognized color. The hood should be complete, covering the head, throat, chest, and shoulders, except in light colored markings where a pale colored throat and chest is allowable. All white areas should be free of spots or brindling.

CAPPED – Capped rats can be exhibited in any recognized color. Color is not to extend past the ears, should follow the line of the lower jaw bone, and should not extend under the chin. Should have a white spot on forehead, or a blaze. The rest of the body should be a clean white with no spots or brindling.

VARIEGATED – The head and shoulders to be of any recognized color with a white blaze or spot on forehead. The variegation to cover the body from the shoulders to the tail including the sides and tail. Belly fur to be white, devoid of creamy tinge or staining.

BLACK-EYED WHITE – As white as possible, devoid of creamy tinge or staining; any colored hairs to be severely penalized

BLAZE – This marking may be shown in Berkshire, Variegated, or Odd-Eye in any color. A wedge shaped blaze of white should run from the muzzle to the ears including the whisker beds, tapering to a fine point between the ears.“

     NFRS [US] 

HOODED – The hood shall be unbroken, covering the head, throat, chest and shoulders, except in the case of light coloured hooded varieties where a pale coloured throat and chest is permissible. The hood shall be continuous with the saddle (spinal stripe) which should extend down the spine to the tail, with as much of the tail as possible being coloured. The saddle width shall be 1-2cm, dependent on the size of the rat – it must be as even as possible and unbroken. The edges of the hood and saddle shall be clear cut and devoid of brindling. The white area shall be pure and devoid of any yellowish tinge or staining.

BERKSHIRE – (shown in Berkshire/Badger) To be symmetrically marked, with as much white on the chest and belly as possible. The white shall not extend up the sides of the body; the edges shall be clear cut and devoid of brindling. Back feet to be white to the ankle, forelegs to be white to half the leg. Tail to be white to half its length. The body colour shall conform to the recognised colour variety. The white area shall be pure and devoid of any colour or staining. A white spot on the forehead is desirable. Suspenders to be allowed providing they are symmetrical.

IRISH – White equilateral triangle on chest with front feet white and back feet white to half their length. The triangle to be of good size, clear cut and devoid of brindling, not to extend in a streak down the belly but to occupy all the space between the front legs. The body colour shall conform to a recognised colour variety.

ESSEX – To be recognised in any standard colour, remembering that the effect of the gene responsible is to lighten the top colour. The darkest area is along the spine, becoming less intense down the sides of the animal. The gradual fading of colour continues onto the belly which is off white, with no spotting of darker colour. When viewed from above, the fading effect should be symmetrical, having no clear demarcation. The fading effect also to be seen on the legs so that the feet are also off white. There should be no obvious patches of contrasting colour. Pied tails not to be penalised. A head spot is essential; this must be well defined, centrally placed on the forehead and symmetrical.

CAPPED –  The colour not to extend past the ears and to follow the line of the lower jaw bone, it should not extend under the chin. A white blaze or spot on the face, and the rest of the body white. Colour to conform to a recognised colour variety. White area should be pure and devoid of yellowish tinge and staining.

VARIEGATED – The head and shoulders to be of a distinct colour with a white spot or blaze on the forehead. Where a spot is present this should be centrally placed on the forehead, round or oval in shape and no bigger than the rat’s eye. Blazes are a wedge shaped symmetrical blaze of white starting at the nose and extending up the face to the forehead. The blaze to cover the whisker bed and taper to a fine point midway between the eyes and the ears. Markings not to extend onto the cheeks or the eyes. The rest of the upper portion (back, sides and tail) of the rat’s body to be white, evenly marked with patches and flecks of distinct colour, the colour to conform to a recognised colour variety. Underside (including belly, chest and throat) to be white, devoid of creamy tinge or staining.

BADGER – As much of the underside of the rat as possible to be white, including belly, chest, throat and underside of the legs, the white not to extend up the sides of the body. Back feet to be white to the ankle, forelegs to be white to the elbow. Tail to be white to half its length. The body colour shall conform to a recognised colour variety. The white area shall be pure and devoid of any colour or staining. The defining feature of this variety is the blaze. This is to be a wedge shaped symmetrical blaze of white starting at the nose and extending up the face to the forehead. The blaze to cover the whisker bed and taper to a fine point midway between the eyes and the ears. Markings not to extend onto the cheeks or the eyes.

BLAZED ESSEX – (shown in Essex) Blazed as in badger standard. Essex as in Essex standard.“

 

Keypoints

  • Despite it’s name, the Hooded locus is responsible for the majority of the marking genes we know in rats.
  • The base h allele mutation is recessive and can produce Self (HH, Wild Type), Berkshire (Hh, Irish (Hh), hooded (hh) and a number of mismarked in-betweens.
  • Essex is a Dominant Lethal H allele mutation; symbol H^ro.
  • English Irish is similar to Irish but with the marking adorning only the upper chest , and is on it’s own allele h^i.
  • The Notched (h^n) and Extreme (h^e) alleles cause high white spotting in the rat and are often used as safer mutations to breed BEW as well as Capped, Bareback, Masked and Patched among others.
  • Variegated markings are complicated, and seem to be based on a combination of possibly both known and unknown genes and modifiers.

 

A Final Thought


The Hooded locus is one of the first and most important genetic mutations in rats. With it’s large array of allelic mutations and other modifiers and genes it is responsible for a large and unique array of white markings in rats that have become some of the most popularly kept pet rats. In this day and age, it is actually generally harder to find a rat without the h locus mutation.

Bibliography

http://imagineratterysa.pbwebs.com/u/imagineratterysa/content/documents/The%20H%20Locus%20explained%20-%20By%20Ronel%20Pienaar.pdf
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1209518/pdf/254.pdf
https://igloorats.weebly.com/aftegninger.html
https://www.afrma.org/pdf/2012wssfp11-21.pdf
https://academic.oup.com/jhered/article-abstract/62/6/357/828486?redirectedFrom=fulltext
http://www.ratbehavior.org/CoatColorMutations.htm#Hooded
https://www.afrma.org/ratmkd.htm#maskedrt