Rat genetics

[Adam Chandler]

I found a very interesting article about what genetically causes different colors and patterns on a rat's coat and just wanted to share.

You can read the article here:http://www.ratbehavior.org/CoatColorMutations.htm

I found this section on the Red Eyed Dilution particularly fascinating:

"Mutations in melanosome formation:

A problem in the lineage of cells leading to melanosomes: the red eyed dilution allele

Melanosomes are tiny little vesicles found inside the pigment cell. Pigments are assembled inside these little melanosomes, which are then transported to the edge of the pigment cell and deposit their pigment in the growing hair.

Melanosomes are actually part of a family of related "cell organs" (organelles) (Orlow 1995, 1998), that includes lysosomes and platelet dense granules. Lysosomes are little vesicles inside cells that contain enzymes involved in breaking down metabolites (waste). Platelet dense granules are found in blood platelets (they store and secrete adenosine nucleotides and serotonin). Defects in platelet dense granules lead to poor blood clotting and prolonged bleeding.

These three kinds of organelles, melanosomes, lysosomes, and platelet dense granules, all descend from a common ancestor organelle. Therefore, any mutation that affects this common ancestor will affect the descendants. The recessive red-eyed dilution mutation (r) has just this effect.

The red-eyed dilution mutation interferes with normal development of these organelles. This leads to abnormal transport of melanosomes within the pigment cell, which causes reduced pigment deposit in the hair and eyed -- hence the red eyes and pale fur. Homozygous rats with red-eyed dilution also have abnormal platelet function, called Platelet Storage Pool Deficiency (SPD) (LaVail 1981, Prieur 1984). In rats with SPD, platelets have defective secretion of clotting mediators, which leads to profuse bleeding (Raymond and Dodds 1975, Tschopp and Baumgartner 1977, Kirchmeier et al. 1990, Magro et al. 1992).

Red-eyed dilution is quite different from pink-eyed dilution, thoug the animals may have a similar appearance (though rr rats have reddish-brown eyes, while pp rats have truly pink eyes (LaVail 1981)). Genetically, however, these are quite distinct mutations that have very different effects.

Examples: An otherwise agouti rat homozygous for red-eyed dilution will be a golden tan called fawn (Prieur 1984)

Note: The red-eyed dilution of agouti isn't the only way to get a fawn colored rat. There is also a separate fawn mutation (f), which reduces pigmentation in both black and blue animals, though its cellular mechanism is unknown. Fawn on a black rat produces a coffee brown animal, while fawn on a blue animal produces a fawn animal (Castle and King 1947).

Other effects: Fawn (rr on agouti) hooded rats are used extensively in research, and have a whole list of associated disorders:

* hypertension (Rudofsky and Magro 1982, Kuijpers et al. 1986, Kuijpers and Jong 1986) leading to:
o proteinuria (protein in the urine) (Kuijpers et al. 1986, Kuijpers and Jong 1986)
o focal glomerular sclerosis (scarring of kidney tissue) (Kreisberg and Karnovsky 1978)
o kidney failure (de Keijzer et al. 1989)
* altered responsiveness of serotonergic mechanisms in the central nervous system (e.g. Gudelsky et al. 1985, Wang et al. 1988). For more details, see Hulilhan-Giglin, 1992, 1993, Chen and Lawrence 2000.
* alcoholism (Daoust et al. 1991, Overstreet et al. 1992, Rezvani et al. 2002).
* high social anxiety and low aggression (Kantor et al. 2000).

Fawn hooded rats have been used as an animal model for human psychiatric disorders involving anomalies in serotonin function, such as:

* depression (Overstreet et al. 1992, Rezvani et al. 2002)
* anxiety (Altemus 1994)
* obsessive-compulsive disorder
* eating disorders

Only the platelet storage disorder discussed above, and a serotonin uptake disorder (Tobach et al. 1984) have been shown to be caused by the red-eyed dilution gene (Hamada 1997, Fugimori et al. 1998, Prieur 1984). Many of these other disorders may be caused by other genes, which have come to be associated with these laboratory lineages of fawn rats (Overstreet and Rezvani 1996, Overstreet et al. 1999, Rezvani et al. 2002).

Human analogues: There are at least 15 mouse analogues, including: light ear, maroon, pallid, pearl, and ruby-eyed. Like red-eyed dilution, these analogous mutations affect melanosomes, platelet storage granules, and lysosomes. However, none of these analogous mutations are exactly the same mutation as red-eyed dilution. In other words, these analogues affect the same process but in different ways (Nguyen et al. 2002, Prieur 1984).

There are several human analogues that show platelet storage deficiency and depigmentation:

Hermansky-Pudlak syndrome (HPS). Individuals with HPS have a range of depigmentation, from white hair and skin to brown hair and skin due to many freckles. Individuals with HPS have decreased visual acuity and lung problems (pulmonary fibrosis) and intestinal problems (granulomatous colitis). HPS is caused by a problem in the membrane proteins of the three organelles mentioned above (melanosomes, lysosomes, and platelet storage granules) which result in defective transport. There are at least three different types of HPS (Huizing and Gahl 2002). It is rare in most human populations, but is the most common type of albinism in Puerto Rico. The mouse homologue of HPS is pale ear.

Chediak-Higashi syndrome (CHS). Humans with CHS show profound depigmentation of skin, severe recurrent infections, proliferation of lymphoid tissue (lymphoproliferative disorder) and numbness of the extremeties (progressive peripheral neuropathy). Individuals with CHS have giant melanosomes in their melanocytes and giant lysosomes in their white blood cells (leucocytes). This is a serious condition and many people with CHS die prematurely. CHS is also found in mink, cattle, mice and cats. The mouse homologue of CHS is beige. There is also at least one instance in the literature of beige rats with CHS symptoms (Ozaki et al. 1998)."

Again, you can read more about rat genetics here.

[Adam Chandler]

Found another interesting section, this one regarding hooded rats:

The hooded allele in the rat delays the migration of melanocytes from the neural crest (Figure 1). Consequently, the areas furthest from the dorsal midline -- feet, chest, belly -- don't have melanocytes, and those areas produce depigmented, white hair.

I had been wondering what caused the hooded mutations appearance, and this definitely explains it. It seems the hooded allele prevents the melanocytes that produce pigment from spreading away from their origin at the neutral crest on the back.

What I'm wondering now is if the Black Eyed White (BEW) allele is just a more severe version of the hooded, preventing the melanocytes from going anywhere on the epidermis except the eyes.
Although in some cases of the BEW it seems some melanocytes make it to spots around the base of the ears or spots on the face (dalmatian spotting) Although I suspect this spotting is a sign that only one allele of the BEW gene is present. I suspect a super homogeneous BEW is be pure white (no melanocytes on the epidermis at all) with black eyes. These suspicions are something I hope to prove in the future with my BEW breeding project.

[snakesRkewl]

We have bred Pure white BEW X almost pure white BEW and ended up with about 3/4 pure white BEW's a fun pairing we have been doing for several litters now.

I love playing with all of the red eye recessives, I'm not a huge fan of red eye dilutes but pink and Ruby eyed dilutes make some killer "morphs"

Minks, burmese, fawns, silvers and many more colors are available because of those dilute genes.

[Adam Chandler]

We have bred Pure white BEW X almost pure white BEW and ended up with about 3/4 pure white BEW's a fun pairing we have been doing for several litters now.

Ah, so it seems it is a simple co-dom trait. I'll be breeding a spotted BEW to another spotted BEW. I'm hoping to get roughly half pure BEW's, for hold backs

I love playing with all of the red eye recessives, I'm not a huge fan of red eye dilutes but pink and Ruby eyed dilutes make some killer "morphs"

Minks, burmese, fawns, silvers and many more colors are available because of those dilute genes.

PED's and RED's do seem to do pretty interesting things to other morphs.
I've got a pink eyed dilute project starting up, I think a good silvery looking Champagne is one of the coolest looking rat morphs around.

I haven't messed with any red eyed dilutes yet. Although I did get this rat on my most recent order of feeders:


It doesn't show up very well in the pic but if you look very closely at the eyes they seem to be a very dark maroon. Is this a Red or Ruby eyed dilute?

[Rhasputin]

On a semi-related note, I am noticing co-dominant tendancies in my ASF ruby eyed genes.


Are red and ruby eyes 2 different things in rats?
I know in mice, red/ruby is the same thing that can come in many shades, but the same gene is causing it. Pink eye being separate.


But what I just read here seems to suggest red and ruby in rats are 2 separate genes?
This might help me in figuring out the ruby co-dom stuff in ASFs if I know more.

[snakesRkewl]

There are 3 red eye colors, pink, red and Ruby and they all dilute differently but all are considered red eye dilutes

A fawn, which the OP's newest ratty looks like is an agouti diluted from having ruby colored eyes.
A black rat with pink colored eyes is a champagne, a black rat with red colored eyes is a beige and a black rat with ruby eyes is called a Buff I guess, I'm not sure I've made any.

[Rhasputin]

So how many genes are there in rats?
I know ruby, I know pink. . . Red is or is not a separate gene?

I always thought it was an encompassing term, like it is in mice.

[snakesRkewl]

Nope red is it's own color.

How many genes, hmmm, good question.

All colors including black are recessive except Agouti.
All red eye colors, pink, red and ruby are recessive traits.
BEW I believe is Dominate(correct me if I'm wrong) as is Agouti.
Colors are either black or agouti or diluted black or diluted agouti.
White is caused by the high white gene.

I don't and haven't bred mice so I'm not sure how their genetics work, trying to keep up with snakes and rats is a full time task, haha

[Rhasputin]

I mean how many eye colour genes specifically?

Like for mice it's p/p for pink eye dilution and ru/ru for ruby eye dilution. Other than that, there are no genes that effect the eyes specifically.
But there are some coat dilutions that can effect the eyes (not like how pink eye will lighten a coat, but the exact opposite, a coat gene will lighten the eyes) but I'm not talking about that stuff, nor do I know if there are any genes like that in rats.

This is getting confusing!

[snakesRkewl]

I mean how many eye colour genes specifically?

This is getting confusing!

Sorry I'm not up on my punnet square

There are 4 eye color genes, black and the three red's

As far as coat colors effecting eye color I believe only the high white gene does that