What Is an Allele? Definition and Dog Examples
An allele is one version of a gene. Here's what that means, why a dog carries two alleles of most genes, how one gene can have many alleles across dogs, and examples from dog coats.
By PuppyGenes · How we research and write our guides
An allele is one version of a gene. A dog inherits two alleles of most genes, one from each parent, and the two can be the same or different. Different alleles can change a trait: every dog has the FGF5 gene, but a dog with two long-hair alleles of it grows a long coat, while a dog with the usual allele keeps a short one.
The short version
- One version of a gene: the gene is the place and the job; the allele is the version.
- Two per dog for most genes, one from each parent.
- Many in the population: a gene can have several alleles across dogs, even though each dog carries at most two.
- Differences in the DNA: alleles differ by variants, from a single DNA letter to a larger insertion.
- Dominant, recessive or in between: alleles differ in how many copies it takes to show.
One gene, many alleles
Some genes have several well-known alleles. The ASIP gene, behind many coat patterns, has four main alleles, usually written ay, aw, at and a: sable, wolf-like agouti, tan points and recessive black, in that order of dominance, as a 2011 study described. A dog carries two of the four and shows the pattern of the more dominant one. Our coat colour hub explains how ASIP works with the other colour genes.
FGF5 is another example. Researchers first found one long-hair allele, then a 2013 study found several more. All of them are recessive, and a dog with two different long-hair alleles still grows a long coat. Our guide to long coats has the details.
What makes alleles different
Alleles differ because their DNA sequences differ. Those differences are called variants. Some alleles differ by a single DNA letter, called a SNP. Others differ by a larger change: the furnishings allele of RSPO2 carries a 167-base-pair insertion, and the merle allele of PMEL carries a short insertion of its own. Our guides to furnishings and merle explain both.
How alleles are written
Breeders and labs often write a dog's two alleles as a pair of letters. For a simple dominant and recessive pair, a capital letter usually marks the dominant allele and a lower-case letter the recessive one, so a dog might be written FF, Ff or ff for furnishings. Our guides to dominant vs recessive genes and heterozygous vs homozygous explain what each combination means.
Frequently asked questions
- What is an allele in simple terms?
- An allele is one version of a gene. Dogs carry two alleles of most genes, one from each parent, and the pair decides how the gene affects the dog.
- What's the difference between a gene and an allele?
- A gene is a stretch of DNA with a job, at a fixed place in the genome. Alleles are the different versions of that gene. Every dog has the FGF5 gene; which alleles it carries helps decide whether its coat is long or short.
- How many alleles does a dog have for each gene?
- Two for most genes, one from each parent. Males have a single X chromosome, so they carry just one copy of most genes on it.
- Are alleles and variants the same thing?
- Nearly. A variant is a specific difference in the DNA sequence, and an allele is a version of a gene defined by the variants it carries. People often use the words interchangeably.
From general to personal
See how this applies to your dog specifically.
Our at-home Complete Dog DNA Test adds your dog's own results to these tips across six report sections: breed ancestry, coat colour, physical appearance, temperament and size predictions, genetic diversity and oral microbiome. The report does not include genetic disease or health screening.