Chinchilla Genetics Definitions
Anyone considering getting in to the business of breeding chinchillas should have a good understanding of genetics and how they related to chinchillas. The following is a list of terms and their definitions that should prove to be a good introduction.
ALLELES – An allele is a pair of genes (for the same trait), occupying the same position on chromosome pairs. In this case I will only be discussing alleles for color traits, but there is much more to consider when breeding chinchillas – size, coat quality, conformation, temperament, congenital disease, etc. Realize that alleles can arise through mutations, when the DNA making up a gene is reorganized and the gene produces a different outcome, hence the appearance of new mutations over the years.
CARRIER – An animal is referred to as a “carrier” of one or more recessive color genes if it carries a heterozygous or polygenic allele with one or more dominant genes and one or more recessive genes. For instance a TOV/White Mosaic/Violet carrier has a gene structure of dominant TOV + dominant White + recessive Violet. The violet color won’t show phenotypically, but the animal is a Violet carrier and may throw that gene when bred.
CO-DOMINANT GENES – When two or more dominant genes exist polygenically. Some examples are:
Velvet + Beige = Brown Velvet (TOV Beige)
Beige + White = Pink White (or Beige Mosaic)
Velvet + White = TOV White (or Black and White)
Velvet + Beige + White = TOV Pink White
CO-RECESSIVE GENES – When two or more recessive genes exist polygenically, like Violet + Sapphire = Violet Sapphire
DOMINANT GENE– A gene whose trait will develop in the offspring even though it is present in the genetic material of only one of the parents, hence heterozygous in the offspring. A dominant gene will mask the effect of recessive or incomplete dominant genes. The dominant genes for color are Velvet (TOV, Touch or Velvet, or Black), Beige, and White. Standard is recessive to them. All of these, as well as Standard, are dominant to Charcoal, Violet, Sapphire, and Recessive Beige which are all recessive to everything. White is actually an incomplete dominant gene, hence the ability of the underlying Standard or Beige gene to show through in different degrees – Wilson White, White Mosaic, or Silver. Ebony is a weakly dominant accumulative gene and is therefore expressed to varying degrees (depending upon how many generations of Ebony are bred in) with either dominant or recessive colors.
GENES – The basic unit of heredity. Heredity traits are controlled by pairs of genes in the same position on a pair of chromosomes. These gene pairs, or alleles, may both be dominant, both be recessive, or may be polygenic.
GENOTYPE – The basic hereditary combination of genes in an organism. This is not to be misconstrued as “the parents necessary to produce a certain color”, as several different combinations could possibly produce the desired color of offspring.
HETEROZYGOUS – Heterozygous alleles are gene pairs consisting of two or more different genes.
HOMOZYGOUS – Homozygous alleles are gene pairs consisting of two of the same gene. Some genes cannot exist in the homozygous state due to a lethal factor (i.e.. White and Velvet).
INCOMPLETE DOMINANT GENE – A dominant gene whose trait is expressed in varying degrees with other genes. It may blend with or only partially mask other genes. White is an incomplete dominant gene for color in chinchillas. In combination with Standard Gray the result is either White Mosaic, Wilson White, or Silver. In combination with Beige the result is Pink White with varying patterns of Beige coloration. When combined with homozygous recessive colors (i.e.. White + Violet, White + Sapphire), the recessive color trait will appear in varying degrees. Beige also seems to have an incomplete nature as homozygous recessive colors will be visible with it.
WEAKLY DOMINANT ACCUMULATIVE GENE – A gene whose trait is expressed polygenically even in the heterozygous state with either dominant or recessive genes in varying degrees, depending upon how many generations of this gene are bred into an animal. Ebony is an example of this.
LETHAL FACTOR – This term refers to the inability of certain genes to exist in the homozygous state. The two lethal genes for color involved in chinchillas are White and Velvet (also referred to as TOV – “Touch of Velvet” – or Black, not to be confused with Violet or Ebony). If a homozygous allele of White + White or Velvet + Velvet results from a breeding, the embryo will never develop but be reabsorbed by the mother. It has been said that this may result in a blocked uterine horn (chinchillas have two horns to their uterus that branch out from the cervix).
PHENOTYPE – The physical appearance or makeup of an individual. A group of individuals who resemble each other phenotypically may differ in genetic makeup. Conversely, a group of individuals who are identical for color genotypically may differ phenotypically. This is often the case when the weakly dominant ebony gene is present.
POLYGENIC – Pertaining to or caused by several genes. Traits that are determined by a series of gene pairs are referred to as polygenic. Some common examples of polygenic colors involving co-dominant genes in chinchillas are Pink White (Beige + White), Black Velvet (TOV + Standard), and Brown Velvet (TOV + Beige). An example of a polygenic color involving co-recessive genes are Violet Sapphire (Homo Violet + Homo Sapphire). It gets much more complicated with, for instance, a TOV/Ebony/White Mosaic/Violet carrier or perhaps TOV/Tan/Sapphire carrier where dominant, weakly dominant and recessive genes are involved. The possibilities are almost endless and polygenic traits are very difficult to predict as there are many possible gene combinations when breeding these animals.
RECESSIVE GENE – A gene whose trait will not be expressed in the heterozygous state but will only be expressed in the homozygous state. The recessive genes for color in chinchillas are Violet, Sapphire, Recessive Beige, and Charcoal (sorry – not dealt with here until I learn more).
Note: These definitions were written by Amy of the ChinBin website which is no longer an active website.