If you have no background in genetics, the following concepts in this document could be a bit challenging to fully grasp. It’s best for anyone interested in understanding what is going on with genetics to take a basic course on genetics. It’s never too late to learn! I am working on developing an online course specifically geared towards chinchilla genetics for the chinchilla lovers out there, but for now, a basic course on genetics and reading this document should help you understand the basics.
Tabitha’s credentials: Master’s degree in Biology studying population genetics and systematics, current professor at a community college teaching various biology topics including introductory biology for non-majors.
Duke University has a great online course that works exceptionally well for those with busy lives and an interest in learning at your own pace. Most of the GOOD online courses come with a small, one-time fee that is well worth the price. https://www.coursera.org/learn/genetics-evolution
To start with genetics, we need to understand what the various terms mean and what it is we are looking at. All of your (and your chinchilla’s) hereditary information is stored in DNA. DNA is deoxyribonucleic acid which is, in a basic sense, two long strands of small biomolecules called nucleotides. There are four types of nucleotides in ALL of your DNA, these are Adenine, Thymine, Cytosine, and Guanine. Like most small molecules put into a chain in living organisms, you need VERY few of them to make almost endless combinations. Each nucleotide is complementary to one other nucleotide and these are paired together to make two complimentary (exact opposites of each other) strands that will wind together into the characteristic double helix of DNA. These exact sequences of nucleotides that make up DNA are what gets passed down to offspring through the gametes (sex cells) in the form of sperm and eggs. Now, for the DNA, only certain portions have nucleotides in particular sequences that code for the DNA sequence to be read and translated into proteins. The proteins then become the physical expression of that sequence that we call a phenotype. In comparison, we call a single sequence of nucleotides a gene, and the combination of genes that make up the phenotype is called the genotype. Onto genes! Genes come in pairs, with one from the father and one from the mother. You can have variations of a single gene (like brown eye color versus blue eye color) and these variations of genes are called alleles. When two different alleles are paired together and one allele expresses itself in the phenotype while “silencing” the other allele’s expression in the phenotype, the allele is considered dominant. Likewise, if you need two copies of a gene for it to express in the phenotype it is considered a recessive allele.
When alleles are in combination, we refer to the offspring as being homozygous dominant, heterozygous, or homozygous recessive. Homozygous dominant would mean there are two dominant alleles and that animal will produce its particular phenotype of the gene 100% in the offspring making it a true-breeding individual. Heterozygous typically refers to one dominant allele paired to one recessive allele, but can also refer to two different dominant alleles in combination with each other. Hetero simply translates to “different” while Homo refers to “same.” So now, the last combination is homozygous recessive, and I’m sure you’ve guessed, this is where you have two of the same recessive allele.
What happens when you have two different dominant alleles? Which one will be expressed in the heterozygote offspring? There are a few things that could happen in this case. You can get incomplete dominance or codominance. Incomplete dominance is when the two dominant phenotypes will blend together evenly to make an intermediate phenotype that matches neither parent. A case of chinchillas where we have incomplete dominance would be a brown velvet which is neither beige nor black velvet, but an even blend of the two colors. Codominance is when there is a completely even mosaic or patchwork of both dominant genes, where neither is expressed less or more than the other. There is not a good example of this in chinchillas, but blood type is usually the most basic example for this. If you are AB blood type, you have an even expression of A and B sugars on every blood cell. So, how do we as breeders know what our chinchillas can produce for color combinations? A simple understanding of genetics and which of our colors pass down dominantly or recessively! Then, we can perform simple punnet squares to determine the percent chance that each kit born has of being a particular color. It’s important to note here that you CANNOT accurately predict what color a kit will be with certainty and you CANNOT predict how many of the offspring born will be a particular color. The percentages calculated in punnet squares are statistical chances for EACH baby born of receiving certain traits.
The following mutations are known dominant in chinchillas (note that I will ONLY list the common mutations that are PROVEN as their own mutation and not a repeat of an older mutation) 1. Black Velvet 2. Tower Beige 3. Wilson White
***IMPORTANT!!!! The natural, standard grey color of chinchillas is NOT a dominant. This is the WILD TYPE of chinchillas and is the base color that will show through when there are NO MUTATIONS present.***
The following mutations are known recessive in chinchillas (note that I will ONLY list the common mutations that are PROVEN as their own mutation and not a repeat of an older mutation) 1. Violet 2. Sapphire 3. Lowe’s Recessive White/Goldbar/Champagne 4. Black Pearl 5. Angora 6. Curly (linked locus with ebony mutations)
Ebony is not listed above in the colors for one simple reason, it is not really its own mutation. The practice of breeding ebony has been to put every dirty bellied standard and animal with color wrapping to the belly together to produce what we call an “ebony.” A study done over 10 years ago that was basic in nature showed that there are at least 7 different genes that contribute to the ebony coloration we see in chinchillas. Of these 7 genes, some were dominant and some recessive. This is why, you will not hear professional, reputable breeders call an ebony “homozygous” or “heterozygous” because there is no real way for us to know the actual genotype of an ebony animal. Instead, we classify them by “phase,” that is, the amount of expression of the ebony genes in the phenotype. The range from standard ebony carriers (standards with dirty bellies or standards out of ebony lineage), to light ebony, to medium ebony, all the way to extra dark (every hair shiny black) ebony. Likewise, when ebony is mixed with other mutations, we classify the mixes by phase.
I have also not listed the California White Tail (often, incorrectly referred to as fading whites or California recessive whites) as this is not a proven recessive or dominant mutation. It’s not even proven to be a coat color mutation. With my personal understanding of genetics, pigmentation, and coat color expression, I believe this is a mutation that causes lack of pigment production with age. I believe it’s a dominant disorder and if it is bred for heavily and is a pleiotropic gene like albinism, it could lead to health problems just like any other disorder that causes proteins to not be made correctly.
So now, we will do a simple Punnet square to show how you can statistically calculate what percentage your babies have of being a certain color. First, we need to know what our parents are, so for example we are going to breed a black velvet to a black velvet. Black velvet and Wilson white cannot exist in a homozygous state. Both are lethal in the homozygous state, meaning that the zygote or embryo has some expression that is lethal and basically signals the mother to abort the pregnancy and reabsorb the zygote or embryo so that the homozygous kit is never born. So, our genotypes for the parents need to be decided. Remember that genes are in pairs, so you will have one from the mother and one from the father. We denote genes that code for the same phenotype by using simple letters. In honor of Robert Gunning, the developer of the black velvet mutation, we will use the letter “G” for black velvet. An upper case letter will always specify that the allele is dominant and a lower case letter will always specify that the allele is recessive. We write the dominant allele first in the pair to further emphasize that the dominant allele will express over the recessive. So our two black velvet parents will be Gg and Gg genotypes. To do a punnet square, you list the possible alleles that the parents can pass down. Remember that each parent will pass only ONE of their alleles to the offspring.
G g G GGGg g Gg gg
In this punnet square, the offspring possibilities are in bold. You have a 2/4 chance or 50% chance of this pairproducing a black velvet. There is a 1/4 or 25% chance of the pair NOT passing their black gene and thus producing a standard colored offspring. Lastly, in bold and italics is the chance for a homozygous dominant black velvet which is LETHAL. Each successful mating of this pair has a 1/4 or 25% chance of producing a lethal zygote that will never be born.
Now, it’s important to note here that a standard is the “blank slate” of chinchilla. If you had alleles in combination to produce a standard it would, theoretically, look something like this: wwbbggSSVVPPLL Because of how the genotype works for chinchillas with standard being “no mutation present,” each mutation occupies a different locus and can therefore all be expressed in the coat of a chinchilla at the same time. This is how we get colorations with new names, but they are not new mutations. A pink white is a mix of the Tower beige and the Wilson white, while a Blue Diamond is a mix of the sapphire and the violet recessive mutations. A curly-gora is a mix of the angora and curly fur types, while a TOV white is a mix of white and black velvet. With that, I think we can conclude our simple explanation of chinchilla genetics. It’s not deep or super detailed, but it should help anyone getting started in chinchillas get a basic understanding of the genetics behind the chinchilla and give you a start to play around with probabilities. Remember, a punnet square can tell you the statistical chance of what an individual baby might have, but it CANNOT tell you how many of your babies will be a particular color. It’s not a tool to say, “I had a standard kit last litter, so this litter I will get this mutation.” You cannot predict what will be born, only the statistical probability that each offspring has of having a certain phenotype. Each offspring also has a 50% chance of either being male or female.