GENETICS – Dr. Cara Beasley, Ph.,D. Part 1 of 2

Basic Terminology – In most animals there are two copies of every gene, one from the dam and one from the sire.  These genes can either be the standard (wild type), or a mutation.  Multiple sets of genes determine the coat color in chinchillas.  All the colors seen in chinchillas are mutations of the wild type in one or both genes in the various sets of genes.  These sets of genes are passed on independent of the presences of mutations in other sets of genes.  This means that a chinchilla can express two colors at once.  How each set of genes is expressed determines how the colors look when more than one is present.  Two things to keep in mind are Phenotype and Genotype.  The phenotype is the outward appearance of the animal including the color that is seen.  The genotype is the actual genetic makeup of the animal.  While it isn’t currently possible to know the exact genetic make up of each individual chinchilla, it is possible to know the genotype with regard to the color genes if you know the phenotype and the phenotypes of its ancestors.  While the basic colors are fairly straight-forward genetically, the exact shading, coloring, and patterning follow a more complex set of rules than what I am going to explain here.  Email me if you have questions or would like to discuss the more complex genetics.  Some of the terms I will be using:

Dominant color  – a color which is expressed phenotypically whenever at least one copy of the mutated gene is present, ie the color shows up even if there is only one gene in the animal for it.  For an animal to be a dominant color, one of its parents has to be the same dominant color.  When a genotype is written dominant colors are often written as capital letters.  Beige is an example of a dominant color.

Recessive color – a color which is expressed phenotypically only when 2 copies of the mutated gene are present.  A recessive color will not show up if only one mutated gene is present in the animal.  Animals that have a single mutated gene ofhe recessive color will look the same as an animal without the mutated gene for that color.  For an animal to be a recessive color, both parents need to at least be carriers of the recessive color gene.  When a genotype is written recessive colors are often written as lower case letters.  Sapphire is an example of a recessive color.

Dominant lethal – a color which is dominant and so acts like a normal dominant color when one mutated gene is present, but is lethal whenever 2 of the mutated genes are present.  Because of this lethal factor with the dominant lethal colors, animals that carry 2 copies of the mutated gene for this color die early in the pregnancy and so are not seen in the chinchilla population.  Animals expressing the same dominant lethal color should not be bred together, since 25% of the offspring will be non-viable.  Black velvet is an example of a dominant lethal gene.

Incomplete dominance –  a color which doesn’t necessarily express evenly throughout the animal and so also shows whatever other color the animal is expressing, often in patches or splotches.  Even though it is incompletely dominant it still acts like a standard dominant color.  White is an example of an incomplete dominant color.

Homozygous – when both genes in a given pair (set) are the same.  These genes can be either both mutated or both wild type.  Recessive colors are only expressed when an animal is homozygous with respect to the recessive color genes.
Heterozygous – when the 2 genes in a pair are different, ie. one mutated and one wild type.  Dominant colors are expressed in both the heterozygous and homozygous states.

Hybrid colors – colors that involve the expression of more than one pairs of color genes.  These colors are not new mutations, they are merely the combination of colors that already exist.  Each color is genetically independent of each other and so will follow the normal rules of inheritance.  Ie. the genotype will still be clear even if the phenotype looks different from any of the single colors involved in the hybrid.  A violet wrap is an example of a hybrid color where both the violet and the ebony genes are expressed.

Wild type – The characteristics shown when modifying mutations are not present or are not expressed in the case of recessive mutations.  Standards grays are the wild type color in chinchillas.

Standard Gray – Genotype bb-bvbv-CC-ee-GbGb-SS-VV-ww –  Animal appears gray color, with the darkest part at the top of the back and neck, lightening down the sides to a bright white belly.  Standard grays can range in color from very light to very dark that look almost like black velvets.  The standard gray is what can be considered the wild type color in chinchillas, meaning that it is the color that appears when no mutated or modifying color genes are expressed.  Regardless of shade, all standards should be a clear gray with a blue cast and a bright white belly, rather than a gray with a red or yellow cast.  A pure standard bred to a pure standard will always produce pure standard offspring.

Dominant Colors

Beige – Genotype Bb or BB – Animal appears brown in color, the color should be more of a blue, clear brown rather than a red, muddy brown.  Beige is a dominant color that can occur in either the heterozygous or homozygous state.  Homozygous animal tend to be lighter in color than the heterozygous animals.  The eyes of the animal tend to range from dark red, almost black, to a light red, almost pink color.  Brown eyed beiges have been reported, but it is unknown whether or not they were truly brown or if the lighting made them appear so.  The beige described here is the most common type of beige, also known as the tower beige.  Other variants on beige exist and can be recessive, but they deal with different pairs of genes and so can be treated separately.  Because beige is a dominant color, a homozygous beige animal will always produce beige offspring.  A heterozy
gous animal will produce offspring of which 50% are beige and the other 50% are standards when bred to a standard.  The beige gene can be expressed along with any of the other color genes, giving rise to hybrid colors such as pink white (beige and white cross), tan (beige and ebony cross), brown velvet (beige and black velvet cross), beige violet (beige and violet cross), and beige sapphires (beige and sapphire cross).  Other hybrids involving more than 2 colors are also possible.

White – Genotype Ww – Also known as white mosaic, silver, panda, or Wilson white.  White is an incomplete dominant color that is also a dominant lethal.  Because white is an incomplete dominant color, white animals often appear with patches of color on a predominantly white coat.  The white should be a good clear, blue white rather than a creamy, orange-ish white.  The patterning on whites varies widely from the completely white animal to those that are a uniform silver color to those that are widely marked with patches and splotches.  The markings on a white are always whatever color is being expressed in addition to the white, be it standard, beige, ebony, violet, or sapphire.  Whites that also express the black velvet gene often have a mask that shows on their face regardless of how heavily mark the rest of the body is.  The markings of a white appear to be controlled by a couple of genes in addition to the white that are carried, but not seen without the white gene present.  Because white is a dominant lethal, no white animals, even hybrid whites, should be bred together because 25% of the offspring will be non-viable.  For an animal to be white, one parent must also be white.  Other variants of white, caused by mutations to other pairs of genes have been reported but they are not nearly as common as the Wilson white.  The most common white is the one in which no other color is expressed, it is a cross between a standard and a white and is referred to by the names listed about.  Hybrid colors of white include ebony white (white and ebony cross), TOV white (white and black velvet cross), pink white (white and beige cross), white violet (white and violet cross), and white sapphire (white and sapphire cross).  Other hybrids involving more than 2 colors are also possible.  All hybrids with white genetically count as white and will pass on the white gene to their offspring the same as a normal white.

2 Comments

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  1. Wonderful blog you have here but I was curious about if you knew of any msaesge boards that cover the same topics talked about in this article?I’d really love to be a part of online community where I can get comments from other knowledgeable individuals that share the same interest. If you have any recommendations, please let me know. Bless you!

  2. Hi there. I would like to discuss some more in depth genetics with you specifically the patterns seen in whites. 3 patterns I have seen pop up most are a panda pattern, random dark splotches, and face blazes. How do you think these alleles are passed? The animals obviously have to be white to express them, but do we think the “non whites from these lines “carry” these genes and play a roll in it being expressed?

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