Understanding genetics is an important part of breeding. If you breed an american blue with a russian blue, you may be disapointed when you get all black babies. Of course, the first things you should consider are temperament and health. What is the point of having a pretty, neat colored rat if it's mean and dies young? I am by no means an expert in genetics. It's just a subject I happen to love......and I am a science nerd (yes, I'll admit it...since it will probably help me to get in to medical school). If I am wrong on any of this, please e-mail me as I always love learning :-) 

All rats are either agouti or non agouti based. An agouti rat has bands on it's fur....meaning, the hair will not be completely 1 color throughout. Black rats are non-agouti based....their hair should be completely black with no other coloring on the individual hairs. It's difficult to explain it, I hope that made sense. :-)  

Genes can be dominant or recessive. Dominant genes are signified by capital letters ex:agouti is  'A'. Recessive genes are signified by lower case letters ex: recessive dumbo is 'du'. If a rat inherited a dominant gene, it will express itself. If a recessive gene is inherited, it will only be expressed if the rat is homozygous for it.....meaning has 2 copies of that gene. Everyone inherits genes from their mother and father, so there will be 2 genes that are inherited. A rat cannot display a recessive that is not at least carried by both parents. Here are some of the genes we deal with at our rattery...

Aa (heterozygous agouti) or AA (homozygous agouti) - agouti

d d (russian blue will not be displayed unless homozygous) - russian blue

du du - dumbo ears (homozygous)

Dudu or DuDu - standard ears

r r - RED dilute

m m - mink

Pepe - pearl....PePe is lethal in utero, so no rat is homozygous pearl. Pearling is dominant and needs mink (mm) to be displayed. A rat can have the Pe gene and not display it because of a lack of mink (mm).

MeMe or Meme - merle is dominant. Lighter colors like pearl are needed to display the merling.

Rere - Rex coat

ReRe - double rex....2 copies of the rex gene produces double rex. A 'patchwork' hairless.

rere - standard coat

hrhr - hairless.

Veve - velveteen, dominant like the rex.....not sure of the letter designation?

VeVe - double velveteen, patched hairless like the rex but has a tendency to stay more furred.

                                                                                                                                                                                                                                                                                                                          

Since genes are inherited from both parents, how do you figure out what will be in a litter? Here is an example of a breeding between a dumbo rat and a standard eared, dumbo carrier.

Dumbo rat - dudu    x     Standard eared dumbo carrier    Dudu               

                                   du                       du

Du                           Dudu                   Dudu  

du                            dudu                   dudu                                      

So    50% will be standard eared dumbo carriers  Dudu                                                                       

         50% dumbos dudu

 

What about coloring?

You already know that rats are agouti or non-agouti based. To get different colors, dilutes are added into the mix. This is where RED (red eye dilute), PED (pink eye dilute), mm (mink), dd (russian blue), gg (american blue) etc., come in. Note: the dilutes are recessive. A rat cannot display them unless they are homozygous, meaning both parents at least have to carry it.

Non-agoutis- the colors are abbreviated cause I'm lazy :-)

Russian blue (RB) is a black rat with the RB dilute: aa dd

Blue beige would be adding RED dilute: aa dd rr

Beige is black with RED dilute: aa rr

American blue (AB): aa gg (different dilute than russian blue)

Russian silver: aa dd gg (would have to inherit both blue dilutes...parents would be black, both from an RB and AB parent)

Mink: aa mm

Chocolate: aa bb

Platinum: aa gg mm (mink based) or aa gg rr....I'm not 100% sure on this one.  

Pearl: aa mm Pepe

Agoutis- second gene is unknown unless you know the parents or offspring, so it will be designated with a -- (unknown) 

fawn: A --  rr

Russian blue agouti: A-- dd

Cinnamon: A-- mm

Cinnamon Pearl: A-- mm Pepe

There are more and I'll eventually update the page when I get time. If you have any questions, feel free to email.