Genetic Oddities

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Genetic Oddities


It’s unclear what genetics go into creating odd-eyed mice. It could be caused by the unstable expression of a gene on the C-locus, or could be some form of chimera (an organism that contains cells or tissues with different genotypes).Breeding of odd-eyed mice produces odd-eyed offspring, so there is clearly some inheritable genetic component of this trait.


Transgenic mice have either been liberated from a lab, purchased from a laboratory supply house, or are descended from mice who have. These mice contain segments of genes from other species and were originally created for experimental study.Since there really is no way to determine what genes are present in any transgenic mice other than those purchased directly from a laboratory supply house, a whole range of oddities may be possible with these guys, some of which are discussed below.Transgenic mice can be black, albino, agouti or splashed. Mixed varieties from breedings with other mice may be any colour.

Green mice (GFP)

These are a variant of the transgenic mouse, containing the genes responsible for the green flourescing protein (GFP) in jellyfish. Under certain wavelengths of ultraviolet (UV) light, usually around 488 nm, the skin of these mice will appear to glow green. The hair is unaffected.

Litter with normal and GFP mice
GFP hairless mouse


Tricolour mice are another example of transgenic mice, and it is believed that the patches of colour are caused by a genetic instability. Expression of the tricolouration is linked to the presence of two recessive genes on the C-locus, although breeding has shown that it’s not actually located on the C-locus. The effect of the tri-gene appears to be akin to counteracting the dilution from the recessives on C, thus allowing the hair in those areas to revert back to their non-diluted state. This implies that the tricolour mutation is present in mice with a dominant gene on C, but the effects aren’t noticeable since the reversion colour is identical to that displayed by the dominant C (e.g. black patches on a black mouse). The presence of the tricolour mutation is also not visible on albino mice (c/c) since this combination masks the expression of all other genes.This is a relatively recent development in mouse colouration, and is still being explored; tricolours can be seen with agouti and blue mice as well as the more common cream or brown. 

standard hair tricolour

long haired tricolour

litter of tricolours


Still another variation on the transgenic mouse. The incomplete expression of the tricolour mutation can lead to what is known as a splashed mouse. These mice appear mottled or marbled randomly.

Standard haired splashed


This is an interesting, yet uncommon, anomaly that transmits as a simple recessive.

Earless black tan

Markings and Body Type – Mice

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Manx, or tailless


The dominant state of this allele is tailless, with heterozygotes (T/t) displaying varying degrees of taillessness, from short tails, stubs, or a total absence of a tail. There is also modification to the pelvic girdle in tailless mice, and this aids in distinguishing true tailless mice from those who have lost their tails through mechanical means.This gene is homozygous (T/T) lethal.


This allele produces mice with normal tails.The modifier tn is homozygous lethal.

Coat Types

Note: Unless otherwise noted, all alleles in this section are recessive and the mouse must be homozygous (i.e. two of each) for the trait to be expressed. It has been assumed that the heterozygous form of each locus is phenotypically (i.e. looks like) a normal type.

Long hair


Hair is longer than normal mice, appearing by 3 weeks of age
(21 days). Both guard hairs and undercoat are long, and can produce the appearance of “fluffiness” in some mice.




The coat is soft and extremely shiny; the sheen making it appear
as if made of satin. Has been linked with a genetic disorder which causes babies to wither and die between the 7-10 day stage of growth.




This allele creates a kinky coat, with every hair appearing crimped. Often the hair will lose this crimping by adulthood, which leaves them mouse appearing almost identical to a standard coat.

Adult frizzie




The hair is thin and wavy or curly, as are the whiskers. Not to
be confused with a true hairless since the hair, while thin, is
present. Mice will retain the curly hair throughout their lives.


Longhair fuzzy


Rex or Astrex


This allele is dominant. The hair is thick and wavy with wavy or curly whiskers. They appear almost like little sheep when young, but will lose much of the curl as they age, although they do retain
a wavy coat as adults.Long haired rex mice (Re/* go/go) are referred to as Texel.






This allele is dominant. It produces a curly coat, but as the mouse ages the coat loses its curl and adult mice simply appear




Hairless mice initially develop a normal coat at the same time
as their regular siblings, but will lose it at the follicle level after about 10 days of age. Whiskers may or may not be shed. Some
hair will appear and be shed for the first few months of life, but
eventually the mouse will be continually hairless. The skin may
or may not be wrinkled.These mice are susceptible to cold temperatures and may suffer from suppressed immune systems, leading to an increased susceptibility to disease. Toenails often display unrestricted growth and may need to be trimmed.


This variant of the hairless gene produces mice with thickened skin
that becomes incredibly wrinkled. These mice are often referred to
as “rhino mice” and the periodic return of hair in the early months is not present in these mice.

Coat Markings



This allele is dominant and produces a scattering of white or very
lightly pigmented hairs throughout the coat.Homozygotes (Rn/Rn) are more definitely marked than heterozygotes (Rn/rn) , but both are equally viable and fertile.Roans with patches of plain black fur are called merle.




Recessive white spotting


Produces varying degrees of irregular white spotting over the entire
body in homozygotes (s/s). Has been linked to megacolon in some
cases.Often a dark mouse which carries this recessive will have a small pink patch on or near the end of the tail.

Carrier with white tail spot


Dominant white spotting


This is a dominant allele. A mouse with this gene will appear
variegated or marbled.This is homozygous (W/W) lethal, and mice with this genotype will appear as black-eyed whites (BEW) and will die shortly after birth.

Sex-Linked Brindle


Heterozygous mice will appear patchy or mottled orange and black,
similar to the appearance of tortoishell cats. Usually black is the predominant colour. This allele is dominant.This gene is lethal in males and homozygous females both of whom usually die within 2 weeks after birth.



Double Punnett Form

Enter the alleles for both parents in the boxes below. For unknown
recessives, enter *.

First Allele
Second Allele
Father 1:

(dominant, if exists)
Father 1:

(dominant, if exists)
Father 2:
Father 2:
Mother 1:

(dominant, if exists)
Mother 1:

(dominant, if exists)
Mother 2:
Mother 2:

Simple Punnett Form


2012-11-29 10:43:34 mugwumpr




Mongolian Gerbils were first introduced to the pet industry in 1964. Their value as pets was soon appreciated and they are now found in pet shops around the world.  It is illegal to purchase, import, or keep a gerbil as a pet in some areas due to the threat they pose to indigenous ecosystems and existing agricultural operations.

A common misunderstanding when purchasing a home for pet gerbils is that they can live in housing designed for hamsters and mice. This type of housing is unsuitable as they require the ability to be able to dig tunnel systems. The plastic structures of hamster and mouse cages are inappropriate for gerbils as they can gnaw through it very quickly. Plastic can cause serious health issues for the animal if ingested, therefore many owners refrain from having any plastic in the tank and rely entirely on wooden toys. While there is conflicting information from gerbil societies regarding habitat size, a common rule of thumb for aquaria is 10 imperial gallons per gerbil.

(image courtesy of Wikipedia)
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Fancy rats

2012-11-29 10:42:05 mugwumpr

fancy rats



Specially bred as pets since the 18th and 19th century, fancy rats now come in a wide variety of colours and coat types and there exist several rat fancy groups worldwide. Fancy rats are commonly sold as pets in stores and by breeders.

Domesticated rats are physiologically and psychologically different from their wild relatives, and—when acquired from reliable sources—they pose no more of a health risk than other common pets. While fancy rats are subject to different health risks than their wild counterparts, they are consequently less likely to succumb to other illnesses prevalent in the wild.

(image courtesy of Wikipedia)
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Fancy mice

2012-11-29 10:40:45 mugwumpr

fancy mice




Fancy mice are mice that have been selectively bred as pets or for show. They can vary greatly in size, from small pet mice that are approximately 16–18 cm (6–7 in) long from nose to the tip of the tail, to show mice that measure 30 cm (12 in) nose to tail. Pet mice weigh about 25–40 g (0.9–1.4 oz) but large show mice can weigh up to 100 g (3.5 oz).

Human-directed artificial selection in fancy mice has created a wide variety of colors and patterns. These include black, chocolate, blue, white, cream, lilac, red, fawn, champagne, cinnamon, golden agouti, silver agouti, silver and dove. All mouse standards fall into one of five categories: Selfs (one solid color all over), Tans (mice of one solid color on the top with a tan belly), Marked either in Even or Broken patterns (spotting of a standard color on a base of white) and a miscellaneous category.

(image courtesy of Wikipedia)
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Welcome to the new site!

2012-10-12 15:05:39 mugwumpr

The old platform that Pet Rodents was running on had become old, tired, and largely broken.  Since the removal of the forum, the need for that particular platform was gone, and some of the components of it had stopped working as they should.

So, since I had to pour a significant amount of time into updating the website and plugging the ever-increasing number of holes that were manifesting themselves out of the ether, I decided to move to a spanky new platform that’s a breeze to maintain, and a whole lot more secure.  It should also load faster than ever before.

And, since I was going to all that trouble, I decided to make it look all shiny and new at the same time.

So, that about sums up everything.  If you find something that’s broken, please leave a comment and I’ll do my best to get it fixed up quickly. Meanwhile, enjoy!!

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Okay, I surrender

2012-06-04 21:01:57 mugwumpr

I’ve been fighting a losing battle against spambots, and I’m sorry, but all the automated solutions have been circumvented and I simply don’t have the time to clean things up manually given that the spam has started arriving wholesale instead of the trickle that it had been.  I had wanted to leave the forum up because of the valuable information that it contains, but until I find a way to prevent either registration or the adding of new posts, I’m afraid that’s just not going to be possible.

The website itself will remain and will be added to from time to time.  If I can find a way to make the info on the old forum available again I’ll do that, but I wouldn’t recommend any breath-holding on that account.

It was a fun ride while it lasted!  Good luck to all of you who participated and contributed to making this a very special place.

Happy mousing!


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Enter the alleles for both parents in the boxes below. For unknown recessives, enter *.


Father 1: (dominant, if exists)
Father 2:
Mother 1: (dominant, if exists)
Mother 2:

The Colour Basics – Mice

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Please note that these pages are the result of a LOT of hard work by the people at PetRodents, unpaid work at that, and all text and images are copyrighted. If you really like what you see, please link to us so these hard-working folks get the credit they so richly deserve for this labour of love. Thanks!

A locus

This is the place where the base colour of the mouse is established


Yellow is the most dominant colour; mice with this gene are prone to obesity. Yellow mice can vary in colour from light yellow to red, depending on the presence of modifiers; this gene is lethal when it is homozygous (Ay/Ay), so all yellow mice will be heterozygous (Ay/_).
Yellow variations


Brindle is dominant to all but yellow (Ay). A typical brindle will be yellow with black or agouti stripes, resembling a tiger; however, the appearance of brindle mice can be  altered by the presence of dilution on other loci. Brindle is also prone to obesity.
Tiger Brindle


Tan is co-dominant to both Yellow (Ay) and Brindle (Avy); these mice will have no stripes on their undersides.
Chocolate Tan


Agouti (A) is the colour of wild mice. The hair consists of a black base with yellow banding on each hair, producing the visual impression of a multi-hued brown.


Non-agouti mice (a/a) lack the yellow banding on the hairs, as in agouti mice (A/_), and therefore appear black. They may have white hairs on their sides and bellies.


Extreme non-agouti mice (a/ae) lack any white ticking, and display black ears, feet and tail. These mice are known as “extreme black” or “super black”, and are very rare.
Extreme black

B locus

This determines whether there is brown dilution


Full colour intensity; no dilution effects present.


Brown dilutes black pigment to chocolate and can also have an effect on the eye color making them very dark ruby.Although yellow mice with a black or brown background look the same, brighter yellows are found with the chocolate background.A brindle mouse with brown dilution (Avy/_ b/b) will appear reddish with brown stripes.An agouti mouse with a chocolate background (A/_ b/b C/_ ) has the black bands in its fur brown, a color we call cinnamon.A non-agouti mouse with a chocolate back ground (a/a b/b C/_) is a brown colored mouse we call chocolate.

C locus

This determines a variety of dilution effects which affect all colours


Full colour intensity; no dilution effects present.


Chinchilla dilution (cch)Yellow mice with chinchilla dilution (Ay/_ cch/cch) are a beautiful cream color. These mice can be selected to be bone, or cream depending on the modifier genes present.A chinchilla diluted agouti (A/_ B/_ cch/cch) is a gray mouse with ticking in the fur. It is known as a chinchilla mouse when also paired with the tan gene (A/at B/_ cch/cch) which chinchilla dilutes to white.Black mice with chinchilla dilution (a/a B/_ cch/cch) are off-black colored, somewhat grayer than normal black, but this is very hard to tell unless compared to a full Colored black (a/a B/_ C/_).Although literature states the chinchilla dilution has no effect on chocolate, chocolate chinchilla mice (a/a b/b cch/cch) are also off-chocolate but no where near coffee in color.In tan mice (_/at cch/cch) the tan underside is diluted to white, producing what is referred to as a “fox” mouse.

Chinchillated agouti


Extreme Dilution (ce) dilutes yellow pigment to pure white, and black and brown pigments to beige. Eye color is unaffected.A yellow mouse that has extreme dilution (Ay/_ ce/ce) is a black eyed white.A brindle mouse with extreme dilution (Avy/_ B/_ ce/ce) will be white with pale grey stripes, also known as a White Tiger Brindle.An agouti mouse that has extreme dilution (A/_ B/_ ce/ce) is a very pale uneven beige color, or coffee.A black (a/a B/_ ce/ce) or brown (a/a b/b ce/ce) mouse that is homozygous for extreme dilution is diluted to beige as well.


Siamese dilution (ch) dilutes brown and black fur to an off-white beige but causes the fur to be acromelanistic. This means the fur is temperature sensitive, with the cooler parts being darker than the warmer parts of the body. The eyes are also diluted which are pink eyed at birth and turn dark ruby as the mouse ages.Yellow Siamese mice (Ay/_ch/ch) can be difficult to identify as they won’t show points, but will be a ruby-eyed white.An agouti mouse with Siamese dilution (A/_ B/_ ch/ch) is a dingy-sooty mouse that has points, but does not have an even coat. The tips of the fur are usually dark-tipped.A black mouse with Siamese dilution (a/a B/_ ch/ch) is a Siamese mouse with a beige coat and dark points on the nose, tail, and feet.Chocolate Siamese mice (a/a b/b ch/ch) are beige mice with chocolate points; the points are lighter than those found on Siamese mice.Himalayan mice are Siamese mice which carry albino (ch/c) and have white bodies with points in any standard colour.


Albino is the ultimate dilution gene, as it covers up the expression of any color on the other alleles. Albino on any color is a pink eyed white mouse.Yellow albinos (Ay/_ c/c) and brindle albinos (Avy/_ c/c) still get obese; you will not be able to tell the genetics of an unknown albino except through breeding tests.
Brindle albino


D locus

This determines whether there is blue dilution


Blue Dilution (d) has a strong effect on yellow and black pigments.A yellow mouse with blue dilution (Ay/_ C/_ d/d) are half way between cream and yellow, but have a light tipping on the fur and thus are often difficult to determine just what color they are.A brindle mouse with blue dilution (Avy/_ B/_ C/_ d/d) will appear buff with blue stripes.An agouti mouse with blue dilution (A/_ B/_ C/_ d/d) is an uneven slate gray with light bands which cause it to appear lighter than a non agouti blue mouse.A black mouse with blue dilution (a/a B/_ C/_ d/d) has the fur diluted to a slate gray-blue color known as blue.

Chocolate mice with blue dilution (a/a b/b C/_ d/d)are a warmer gray known as dove.

Blue beside black

E locus

This allows for yellow colouration without obesity


Extension (e) gene is also known as recessive yellow.
This gene is visually the same as Avy, but genetically

Recessive yellows do not have obesity problems, and therefore do not incur health problems and sterility as do dominant yellows.

P locus

This determines if the eyes are diluted from black to pink; also affects hair colour


Black eyes; no dilution effects present.


Pink eye dilution (p) has a very strong effect on black/brown pigment, but none whatsoever on yellow pigments. All mice with this gene have pink eyes, if the eyes are not pink, another gene is responsible for the coloration.

A yellow mouse with pink eye dilution (Ay/_ C/_ p/p) only has the eyes altered as yellow fur is not affected at all. This is a fawn mouse, and a good way to make yellow clear and non-sooty as the pink eyed gene dilutes any black or brown found in the coat.

An agouti mouse with pink eyed dilution (A/_ B/_ C/_ p/p) is a beautiful color called Argente. These mice appear golden but they have a pale gray undercoats with bright gold tips.

A black mouse with pink eyed dilution (a/a B/_ C/_ p/p) has the black fur diluted a warm gray known as lilac.

A chocolate mouse with pink eyed dilution (a/a b/b C/_ p/p) are a pale tan color, and are called champagne.