Cheat Sheet: Understanding the A Locus (Agouti, Tan/Otter, Self) in Rabbits

One of the first color genes to understand is the A Locus, which determines whether the hairs are banded or solid, and what base pattern the color expression of a rabbit is.

First the cheat sheets, then a discussion of "test breeding" to determine genetics; then all breeding percentages for the A Locus.

Most purebred rabbits have at least a three-generation pedigree which can give clues to a rabbit's genetics (or will outright state them; some breeders are excellent at documentation!). Remember that "A" is dominant to "at" and "a," meaning that an Agouti rabbit could be hiding the same or different genes for color...whereas since Self is recessive, ALL Self rabbits are homozygous.

If you do not know the parentage of a rabbit, you can "test breed." For test breeding the A Locus, it is always best to breed the rabbit-in-question to a Self rabbit. Here is an example: I had a doe who had extensive white patterning, and I couldn't visually discern if she was Agouti, Otter (Tan), or Self. I decided to test-breed her to determine her base colorings. I bred her twice, to two different Self bucks. With both bucks, she produced Otters (Tan pattern) as well as more Self rabbits. She did NOT produce any Agouti rabbits; since every rabbit has two genes per locus (one from each parent), it became clear she was an Otter, but heterozygous for Self. 

Had I bred her to a Self and she instead produced 50% Otter (tan) and 50% Agouti, it would prove she was Agouti.

There is something to mention about test breeding: results may vary. There is a reason I bred her twice to two different Self bucks: sometimes, you just get lucky. That doe was genetically an Otter (Tan) carrying Self, BUT she could have produced a litter of entirely-Self rabbits. You can flip a coin a hundred times, and you will rarely get Heads 50% of the time exactly! I usually recommend three test breedings unless the first or second breeding proves the genetics. If after three breedings, the results are consistent, it is safe to assume the rabbit's genetic color.

CLIFF'S NOTES FOR THE A LOCUS:

An Agouti rabbit can be one of three things, genetically: A/A, A/at, and A/a.

A/A = Homozygous Agouti. Two homozygous Agouti (A/A + A/A) will produce 100% homozygous Agouti. NO EXCEPTIONS. 

A/A (homozygous Agouti) bred to a homozygous Tan/Otter (at/at), 100% offspring will be Agouti carrying Tan (A/at). NO EXCEPTIONS.

A/A (homozygous Agouti) bred to a Tan/Otter carrying Self (at/a) will produce 50% Agouti carrying Tan (A/at), 50% Agouti carrying Self (A/a). Visually, the litter will be 100% Agouti; it will be unclear which kits carry Tan or Self unless test breedings are performed down the line.

A/A (homozygous Agouti) bred to a Self (a/a) will produce 100% Agouti carrying Self (A/a). NO EXCEPTIONS.

A/A (homozygous Agouti) bred to an Agouti carrying Tan/Otter (A/at) will produce 50% homozygous Agouti (A/A) and 50% Agouti carrying Tan/Otter (A/at). Visually, the litter will be 100% Agouti; it will be unclear which kits carry Tan unless test breedings are performed down the line.

A/A (homozygous Agouti) bred to an Agouti carrying Self (A/a) will produce 50% homozygous Agouti (A/A) and 50% Agouti carrying Self (A/a). Visually, the litter will be 100% Agouti; it will be unclear which kits carry Self unless test breedings are performed down the line.

at/at = Homozygous Tan (Otter). Two homozygous Tan/Otter rabbits (at/at + at/at) will produce 100% homozygous Tan/Otter. NO EXCEPTIONS.

at/at (homozygous Tan/Otter) bred to a heterozygous Tan carrying self (at/a) will produce 50% homozygous Tan (at/at) and 50% Tan carrying Self (at/a). Visually, the litter will be 100% Tan/Otter; it will be unclear which kits carry Self unless test breedings are performed down the line.

at/at (homozygous Tan/Otter) bred to a Self (a/a) will produce 100% Tan/Otter carrying Self. NO EXCEPTIONS.

at/a (heterozygous Tan/Otter) bred to a Self (a/a) will produce 50% Tan/Otter carrying Self (at/a) and 50% Self (a/a).

a/a (homozygous Self) bred to another Self (a/a) will produce 100% Self rabbits. NO EXCEPTIONS.

Lastly, something to keep in mind is that the percentages listed above are for EACH KIT, not the litter as a whole unless the result is 100% foolproof. This means that each kit in a litter of, say, heterozygous Agouti carrying self (A/a) to Self (a/a) mating, has a 50% chance of being Agouti carrying Self. As such actual litter percentages may vary!

If you have any further questions, please feel free to comment below!