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Staff member
Jan 28, 2009
South Dakota
FAQ - Hetero/Homo


-Written by Silverfall

Heterozygous and Homozygous

When dabbling in chinchilla breeding and genetics, one of the first things you’ll learn is that within each organism is a set of genes (referred to as the genome) and these genes dictate how the organism develops. Both humans and chinchillas (all animals in general) inherit two sets of genes, one from their mothers and one from their fathers. This is advantageous to the species because if you inherit a faulty gene from one parent, chances are good that you may inherit a better one from your other parent. Almost all genes have a counterpart then (the exception being some sex-related genes) and it is when we talk about the relationship between these two genetic partners that we begin to use the terms heterozygous and homozygous.

Homo means the same. Hetero means different. Since all the genes have a specific partner, when you isolate a gene pair from the rest of the genes in an organism, you find one of two things: either the genes will be identical or they will be non-identical (kind of like identical or fraternal twins). When they are identical, they are called homozygous. When they are non-identical, they are called heterozygous.

In chinchillas, you see the term hetero and homo pop up all the time, especially with beige chinchillas. This is because if you isolate the gene pair responsible for beige color, you will find one of two things:
either the chinchilla with have two beige genes or it will have one beige gene and another gene (that doesn't produce beige color). Homo beige is very light and creamy because it is “two parts beige” and has more influence on the coat color. Hetero beige has only one beige gene, so has less influence on the coat and appears darker.

Is it important to distinguish hetero or homo status? Only if you will breed and only if it matters what kind of offspring the parent can produce. A chinchilla that is homozygous for a particular trait can only pass that trait to its offspring. This may or may not be beneficial to a breeding program depending on how you feel about the trait in question. If you want to produce all beige babies or crosses of beige like pink white or brown velvet, then a homo beige would be handy. A chinchilla that is heterozygous for a trait can only pass that trait some of the time. If you want to produce a variety of offspring (in this case both gray and beige), then a hetero beige is a better choice.

The terms homozygous and heterozygous also have some importance when breeding recessive colors. Chinchillas that exhibit recessive coloration are homozygous for those recessive genes. They will always pass one recessive gene to their offspring. Chinchillas that are heterozygous for a recessive gene are referred to as “carriers.” They will not pass that gene all of the time, but are still found useful in recessive breeding.
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