[Show/Hide Right Column]

Standard Genetic Nomenclature for Dogs

Dogs have 38 autosomes plus either XX or XY as Pair 39. Most literature uses a standardized notation of “CFA ##,” where “##” indicates the chromosome on which a particular gene is located. Like the majority of genetic annotation, uppercase letters indicate dominant traits, and lowercase letters indicate recessive traits. Below are some examples of the standard notation format.

CFA 5: E/E
This particular locus (E) is on Chromosome 5, and the animal described is homozygous for the dominant (E) allele for this locus.

CFA 5: E/e
At locus E is on Chromosome 5, this animal is heterozygous. It carries both dominant (E) and recessive (e) alleles for this locus.

CFA 5: e/e
The animal described is homozygous for the recessive (e) allele for this locus.

This annotation can be used either for phenotypes, or to denote incomplete genotypes. Again, E indicates that the dog displays the dominant phenotype, but based on the given information or its appearance, we cannot say whether the dog is E/E, or E/e. Note that the actual chromosomal location has been left off in this example; it is not required to be used.

In dogs there are several loci with multiple dominant alleles. The superscript in this annotation simply indicates an alternative dominant allele for the E locus.

Supplemental Nomenclature

For parts of the Teaching Genetics with Dogs project, we are testing a second supplemental nomenclature. It serves several purposes.

  1. Anyone not yet familiar with specific genes and alleles still can tell which alleles are dominant or recessive to each other.
  2. It helps users remember the relative order of stacked allele series. For example, agouti (a), has several alleles that are dominant or recessive relative to each other. Numbering them helps reduce confusion.
  3. Some web search engines cannot distinguish between genotypes written in upper versus lower case. (For example, searching for "E/E" would retrieve pages and items marked E/e and e/e, not just E/E.
  4. It is an educational experiment. We want to know if it helps improve student understanding.

The supplemental notation is easy to use and understand.

  • The numeric notation is put in parentheses after the letter notation.
  • Simple dominant and recessive alleles are numbered 2 and 1 respectively.
  • Co-dominant alleles have the same number.
  • Alleles are given a 0 (zero) if they are unknown or can be several alternatives. A zero is equivalent to a dash in a text genotype, which is how most geneticists mark unknown genotypes.


  • B locus. Has 2 alleles
    • B/- (2/0) means the dog has a dominant phenotype (B) but we do not know the second allele.
    • B/B (2/2) is homozygous dominant
    • B/b (2/1) is heterozygous
    • b/b (1/1) is homozygous recessive

  • Agouti locus. Has an allele series that is numbered in order of relative dominance.
    • ay (yellow or sable) = 4
    • aw (wolf marking) = 3
    • at (black and tan) = 2
    • a (non-agouti) = 1
    • An example of an annotated genotype would be ay/aw (4/3)

Download print copy of page

Creative Commons License
This text is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License.

Page last modified on Tuesday June 30, 2015 17:17:17 EDT

Show php error messages