Chinchilla GeneticsThe following is a description of what I know about genetics, and a definition of terminology used in describing chinchillas. The descriptions used may not conform to scientific standards, but are provided to help the average person to understand chinchilla genetics a little. Two terms important to understand are heterozygous and homozygous.
Heterozygous - means that the chin carries a pair of different genes. Only one of the genes, the dominant one, is fully expressed, but that chin is still capable of passing on the recessive gene to its offspring. The trait I normally talk about is fur color. A heterozygous beige chinchilla has a dominant gene for beige and a recessive gene for gray. This animal is beige in color, with ruby red eyes. The darkness of the beige can vary greatly. Sometimes the term 'half' can be used as well, as is the case of the heterozygous ebony chinchilla, which is 'half' black and 'half' gray.
Homozygous - This animal has a gene pair for a trait that express themselves the same. This chinchilla possess 2 dominant or 2 recessive genes. A standard gray chinchilla possesses 2 recessive gray genes. A homozygous beige chinchilla possesses 2 dominant beige genes. This animal is a very light beige color, with bright pink eyes.
Standard GrayThe Punnet square is a good way of describing the possibilities of offspring from different breeding combinations. Place the genes of one parent on the top, and the genes of the other along the side of a 2x2 square box. A standard gray chin carries 2 recessive genes (aa). Breeding 2 grays results in only standard grays being produced, as seen in the Punnet square below.
a a |---------| a | aa | aa | |----+----| a | aa | aa | |---------|
Homozygous Beige to a Standard GrayA homozygous beige carries 2 dominant genes (AA). Breeding a homozygous beige to a standard results in all heterozygous beige chinchillas as seen below.
A A |---------| a | Aa | Aa | |----+----| a | Aa | Aa | |---------|
Heterozygous Beige to a Heterozygous BeigeHomozygous beige chinchillas are rarely seen in pet stores. One possible way to get a homozygous beige is through the breeding of 2 heterozygous beiges (Aa). This gives a 25% chance of getting a homo-beige (AA), 50% chance for hetero-beige (Aa), and 25% for a standard gray (aa), as seen below. (Note: The stomach of the normal beige, both hetero and homo, is white in color.
A a |---------| A | AA | Aa | |----+----| a | Aa | aa | |---------|
Heterozygous Beige to a Standard GrayAnother common breeding combination is a standard gray to a hetero-beige (aa x Aa). This gives a 50% chance of getting hetero-beige babies, and 50 % chance of standard gray babies.
a a |---------| A | Aa | Aa | |----+----| a | aa | aa | |---------|
Breeding with WhitesBreeding with white chinchillas requires special consideration. There is a lethal factor involved when breeding 2 white chinchillas together. When 2 white genes meet, it can cause the mother to absorb the baby back into her system, and possibly block one of her two tubes from future breeding. Another possibility is that the baby could be born very weak and die. Any chinchilla carrying the white gene should not be bred to another carrying a white gene, even if they are not pure whites.
The first white mutation of chinchillas occurred on the Wilson ranch, and therefore are called Wilson whites. These chinchillas have the dark eyes and ears, and can be pure white, white with a few gray hairs, white with gray patches (silver mosaic), or appear to be silver in color. The silver is actually an even distribution of white and gray hairs that make the chinchilla appear silver in color. All of these variations have a lethal factor, and should not be bred together.
In my experience of breeding silver chinchillas, they tend to produce silver babies instead of pure white, which means some mutation of the gene has probably occurred.
The white gene is dominant over the standard gray gene. A Wilson white chinchilla carries Wa, while the standard gray is aa as we saw before. Breeding a white to a standard gray gives equal possibility of getting white or standard gray offspring as seen below. The 50% white could actually be any variation of white as described above. Note that the Wilson white only exists in the heterozygous state, as seen below.
a a |---------| W | Wa | Wa | |----+----| a | aa | aa | |---------|
Double Dominance and Linked GenesSo far I have talked about simple combinations of genes where one is dominant over another. There is a concept called double dominance where 2 genes can each make themselves present, such as white and beige, but the standard gray gene is still carried. The best illustration of this comes when breeding the white to a beige. A common result is a white chinchilla, which has reddish eyes and pink ears. The dominance of the white is shown by the fur color, but the dominance of the beige is shown by the ear/eye color. This chinchilla does carry the standard gray gene as well. Instead of being called a Wilson white, these are referred to as beige-whites. Other possible offspring could have a pinkish appearance to them as well, although I have not seen one.
The pink ear/eye color also illustrates another concept of linked genes. The genes for ear/eye color appear to be linked together. This means you probably will never see a white chinchilla with black eyes and pink ears.
Heterozygous Beige to a Wilson WhiteFor this example, let the heterozygous beige be shown as Ba, Wilson white as Wa, the beige-white as WB, and the standard as aa. This breeding combination gives an equal possibility of all 4 of the above colors as show below. Again, variations in color (silvers, mosaics, pinkish tint, mixed beige hairs) may develop, and could lead to further mutation of the genes.
B a |---------| W | WB | Wa | |----+----| a | Ba | aa | |---------|
Homozygous Beige to a Wilson WhiteBreeding the pure beige (BB in this example) with the Wilson white gives a 50% chance of heterozygous beige chinchillas, and 50% chance of the double-dominant white chin.
B B |---------| W | WB | WB | |----+----| a | Ba | Ba | |---------|
Description of Known Genes and their EffectsMost of this information is based on the book A Textbook of Chinchilla Genetics by E. T. Kelly. This book talks about various genes, and their effects on fur, eye, and ear color. The book is over 20 years old, but I have not found anything more recent on chinchilla genetics. Hopefully all the information is accurate. Of the genes I am going to discuss, several of them may be working together, which is why so many variations exist. This discussion does not cover other genetic issues such as size and coat quality of the animal. Also, inbreeding of chinchillas is strongly discouraged. Although inbreeding can bring out the best qualities of an animal, it also can bring out the worst.
The A gene pair mainly controls the appearance of the standard gray chinchilla. It is responsible for controlling the distribution of the black pigment to various areas of the pelt. In the standard gray, this gene stops the black pigmentation from showing up on the belly, thereby giving the standard a white belly. In a charcoal chinchilla, this gene allows the black pigmentation on the belly.
The B gene pair is responsible for the production of the black pigment, which is utilized in the standard gray. A mutation of this gene is what has led to the brown pigmentation which is present in the beige chinchilla. The brown pigment is recessive to the black pigment. This refers to the gene for pigmentation, not overall chinchilla color, which is determined by a combination of genes.
Since genes exist in pairs, various combinations exist in an animal. For example, the B gene existing in the recessive homozygous state of bb gives the brown pigmentation. The Bb and BB give the black pigmentation, but the shading may vary between them.
The C gene pair is responsible for allowing genes A and B to express themselves. If the C gene exists in the recessive homozygous state (cc), the chinchilla will be an albino, showing no pigmentation. This is not to be confused with the beige-white chinchilla. I have never heard of a true albino chinchilla, but they may exist. The normal state of the C gene allows the A and B genes to express themselves as discussed above.
The D gene pair is called a dilution gene. This gene dilutes the coat color in many animals, and is believed to be responsible for the blue hue seen in the coats of some chinchillas, or the lavender hue as well. It is considered to be a recessive gene (dd). This gene may have some effect in the rare chinchillas known as Violets and Sapphires. I have held a Violet chinchilla, and the silkiness and quality of the coat is just amazing. These chinchillas are also recessive in nature.
Another gene that appears to have an effect on coat color is the E gene, which I do not have a very good understanding of. It allows the black pigments to be distributed throughout the entire pelt with the exception of limitations placed upon it by the A gene. Using the standard versus black charcoal example again, it now appears that the A and E genes both have an effect on the overall distribution of the black pigment.
Black VelvetsThe only other knowledge I have of chinchilla breeding is from personal experience or from reading and discussion with other breeders. One mutation that is not too rare is known as a Black Velvet. These animals are black, with a white stomach. These animals have a lethal factor, and therefore 2 black velvets should not be bred together. I have never had a black velvet, but have black ebonies as described in the next section.
EboniesOf all the mutations I have been involved with, breeding the ebonies has given me the most interesting offspring. A homozygous ebony is jet black over its entire body, and has a very silky coat. The hetero-ebony is dark black on the back, and the coat gets lighter along the side, usually showing some gray. The stomach is dark in color, between gray and black in appearance. One variation of the ebony is the black charcoal, which is dark over the entire body, but is a little duller shade of black than the jet black, and does not have the silkiness. They are, however, still very beautiful, and extremely cute. The next sections will describe the offspring of my breeding with ebonies.
Hetero-Ebony to a Hetero Beige, Ebony carrierI have a hetero-ebony male, who was bred from a standard gray and I believe a hetero-ebony. The ebony is dominant over the standard gray. The mother is a hetero-beige, but appears to carry the ebony gene even though she has a white stomach (Remember an animal with a dark stomach carries the ebony gene). She is a dark beige, and the ebony influence appears to have shown up in the hair on her back. The reason I say she carries the ebony gene is because of the offspring she has produced.
Her first litter consisted of a hetero-beige and hetero-ebony, which is no surprise. The 3rd baby of the litter is a brown charcoal, which only can happen if both parents had ebony in their past. She has a beautiful brown coat over her entire body, with pink ears and ruby red eyes. Under the tips of her brown fur, she is much lighter. Her second litter had 2 standard grays, which shows that both of these parents carry the standard gene. Other litters have included black charcoals and a beige which has the dark stomach, so is an ebony carrier. One of the charcoals was much lighter, and appears to have a beige tint to the outer fur, but the fur is much darker under the tip.