AGOUTI AND BLACK

The Foundations of Color

Color genetics in rats is, for the most part, very simple. Inheritance is pretty direct, and most colors are simple double recessives.

However, if you look at any color or standards list (such as our own FancyRatWiki) and you might think otherwise! There are dozens and dozens of named colors, with mystifying and colorful names like Russian Cinnamon, Silver Fawn and Platinum Pearl. With such a plethora of colors to choose from, how can a new fancier sort out how the genetics of color work?

By starting with the foundation, the first color locus, the gene known as "A."

The A gene is dominant in rats both domestic and wild. That means that AA and Aa both produce the same color: Agouti. The gene combination of aa, the double recessive, produces Black.

What is Agouti?

Agouti is known as the "wild coat." When you look at a squirrel, rabbit or rat in the wild, you are looking at an Agouti coat - though in the wild the color will not be as bold and ruddy, it will be blander, greyer and more diffuse, to blend in with the surrounding grasses better.

On an Agouti coat, every hair is multi-colored. The colors form themselves into bands, or ticking, along each hair. In a regular Agouti rat, those colors are black, tan and chestnut brown on a paler grey undercoat. The belly and feet are also much lighter and covered with pale grey hair. The longer guard hairs are black, and so are the eyes.

What is a Black?

Obviously, a Black rat is… well, black! The color should ideally be inky and consistent, and black from the tip of the hair to the skin. The skin itself is also darker - you will notice that pinkies who are Black will have dark, purplish-blue skin, well before they grow a fur coat.

However, Blacks who are poorly selected for color, or who are by-products of the attempt to breed another color and are therefore carrying a lot of recessives, sometimes have a few characteristics that seem very reminiscent of the Agouti from which they came. Their bellies may be lighter and a silverier shade than true black, and their guard hairs may be white, which is known as "silvering."

When breeding for Black, it is important to try and breed for animals as dark as possible, without any white hairs and whose bellies remain as dark as possible through their adult moults. Black rats can also "sun bleach" in direct, extended sunlight, producing a reddish-brown tinge to the fur. Poor coat or strained health condition can also produce brown patches in the fur, which is known as "rusting."

Because of the way the "A" locus works, being one of the few truly dominant color genes, if you breed a homozygous (both genes the same: AA) Agouti to a Black (being a double recessive, Black is always homozygous, aa,) then you will get all heterozygous (one of each gene, Aa,) Agouti babies. Breeding two heterozygous Agoutis together would give you a chance for 50% Black, 50% Agouti babies, before taking other color genes into account.

How do Black and Agouti make all the other colors?

Other color loci on the genetic strand work to "dilute" the color of the hair on the body. Some dilutes, such as Russian and American Blue, work to leach the red out of the coat, leaving behind hairs that are blue-grey or silvery instead of Black or Agouti. Some, such as Beige or the RED dilute, do the opposite, leaching the blue out and leaving a hair that is orange or yellow instead.

Different dilutes act on the hair color in different ways. Some of them even combine with one another - a Black rat who is carrying two recessive genes of both Russian Blue and American Blue (aa dd gg) is a Russian Silver, a color much lighter and brighter than either of the two parent colors.

When breeding for any single color or dilute, it is best to focus on that color in a single bloodline, simply because any extra recessives can wash our or muddy any color, especially more sensitive colors like American Blue and Mink.

Because it is very difficult to clean the recessives out of a bloodline (a single American Blue gene can hang out in a pedigree for a surprisingly long time before unexpectedly popping up in a litter when it meets another!) it is best, when seeking an outcross for a color, to attempt to use a rat carrying as few other recessives as possible. To that end, a Black or Agouti without other recessives can be an ideal outcross, since it brings nothing new into the color genes that are not already there.