Unfortunately, many people who own rats (or any animal for that matter) and decide to breed have not the slightest understanding of basic genetics. They think that a pretty Blue Dumbo mated with their adorable Hooded Fawn will produce an array of wonderfully colored babies. Too many times people fantasize about what the babies will look like and they assume that the most desirable physical traits will be passed on from each of the parents. This is not at all true, and those who have bred without doing their homework will wonder why that beautiful Blue Dumbo and Hooded Fawn produced a litter of 12 standard agouti pups.

Now I'm no geneticist, and I do not claim to be an expert, but I have taken the time to learn about basic genetics in fancy rats. I learn something new everyday. I urge anyone planning to breed to aquire at least a basic understanding of genetics in fancy rats. Why? Because so many times I have run into good hearted pet owners that just decide to breed for the heck of it, and they assume that their much loved and maybe very beautiful pets will produce offspring with desirable characteristics of each parent. They then end up with a litter off all agouti babies (which are very hard to place in my experiences) which don't get adopted out, and unfortunately end up in petshops as snake food.

Personally I love rats, no matter the color. It's their personalities that hooked me. But to many people, a fancy agouti rat looks like a wild sewer rat, and not like the intelligent domesticated pet it really is. If you are going to breed fancy rats be prepared when the rest of the world doesn't share your enthusiasm. We live in a society where "pretty is better", So if you are going to bring innocent creatures into the world, at least give them a head start by making sure that they will have beauty as well as brains. Remember, most people don't buy pets because they are smart, they buy them because they are cute!

In this tutorial I will talk about basic coat color genetics of fancy rats. I will discuss various terms throughout to get you aquainted, and then will go into further detail on how to predict the outcome of particular matings.

As a breeder you will want to produce animals that have desirable quailities. This is why having at least a basic understanding of genetics is vital.

Now I'm not going to go into a full explanation of chromosomes, DNA and what a double-helix is (you should have paid attention in high school!) I will focus only on what is relevant to gaining a basic understanding of genetics in fancy rats.

All creatures are made up of cells which contain chromosomes. Rats have 42 chromosomes in each cell except the sex cells (egg or sperm) which only have 21. So when rats mate, half of the mother's chromosomes are in her egg and half of the father's chromosomes are in his sperm. Therefore the combination of the egg and the sperm form an embryo with 42 chromosomes. The chromosomes are made up of various genes (dominant or recessive) that affect physical appearance. Keep in mind that each egg and each sperm contain a different combination of chromosomes to be passed along, thus the reason why siblings differ in appearance despite them having common parents.

Each gene has a location on the chromosome known as a locus. Loci (plural of locus) define where specific genetic traits are found on the chromosome. Scientists are discovering new loci all the time.

Each locus holds two genes. One gene is inherited from each parent. The genes for a specific trait may be either dominant or recessive, depending on the parents. These dominant or recessive versions of genes are refered to as alleles.

When the same gene (allele), either dominant or recessive, occupies both positions on the locus, this is known as a homozygous trait (The prefix homo means same). For example: A homozygous agouti rat (A/A) has the "A" allele at both positions on the Agouti locus. A homozygous non-agouti rat (a/a) has the "a" allele occupying both postions on the locus.

When the opposite allele occupies the corresponding position on a locus, that trait is said to be heterozygous (The prefix hetero means opposite). An example would be a heterozygous agouti (A/a). The rat will look the same as a homozygous agouti (A/A), but the heterozygous rat will carry the recessive "a" non-agouti allele.

Certain traits are recessive and some are dominant. If a trait is dominant it is represented by a capital letter, and it needs only one dominant allele (heterozygous) to show. If one parent is homozygous for a dominant trait, all the offspring will show that trait. If a trait is recessive, it must be homozygous to show, meaning that both parents must carry the gene for that trait for it to be displayed in the offspring..

Without getting too complex...there are yet other sets of genes known as modifiers or polygenes. These genetic modifiers do not have loci all their own, instead they latch on to compatible genes and alter their effect.(See Locus C). Polygenes are responcible for the intensity of certain traits. Some black rats have a deep jet black appearance, while others have a dull charcoal black appearance. They both display a black coat color genetically, however thier polygenes may vary causing the slight difference in intensity. The same goes for rex coated rats; some being very curly, others with just slightly frizzy hair. You will never get a superb looking animal of show quality from breeding "so so looking" rats. Breeders take animals that possess desirable traits and pair them with others that are genetically compatible and also share desirable traits.

The table below shows a number of recognized rat loci known to affect coloration, hair texture, body structure, etc. Keep in mind that various genes cause similar traits. Ex: the gene(s) responsible for a rat's curly hair may be Cu1, Cu2, Sh, Re, K, or Wv.