Online Open Genetics

Lesson 4 - Advanced Nomenclature

In "Basic Naming", you learned that it's important to have a consistent method of creating gene names and using it to identify alleles. The best symbols communicate information to the reader. Single-letter codes can work, but what if you have several different traits that start with the same letter? And is there a way to let the symbol tell you if the mutant allele is dominant or not? The Basic scheme outlined tells if the allele is dominant, but you might not know, without extra context, whether the mutation is dominant or not.

Enter "Advanced Nomenclature". At first this will take some practice, but most students get the hang of it and find it useful when dealing with multiple traits.

Always underline your gene names when writing them out. If you're typing them, you can underline or italicise them.

In science, it's conventional to set your text apart stylistically so you know when you're dealing with Latin or Greek words, or a special symbol - such as a gene name!

e.g. You should use Alb for a dominant mutant allele, and Alb+ for its wild-type counterpart.

Also note that the second and third letters are always lower case.

Now that we have the freedom to use three letters, let's make the best use of them. Before, if you had a bald mouse with big eyes and broken ear margins, you'd have to get really creative with the single letters you used. You might have to range far for descriptive terms that aren't intuitive, and it makes your analysis harder: you'll have to put everything you come up with through a filter.

Now, however, you can define the gene names as bld for "bald", bey for "big eyes", and bre for "broken ear". Note that each of these symbols indicates the mutant allele of this gene is recessive to wild-type. The wild-type alleles, of course, will have superscript "+" at the end: bld+, bey+, and bre+.

Note also that you have more control of the gene names than this example... perhaps you prefer bal for "bald"?

Finally, note that the gene name is essentially the long form of the mutant gene symbol. Thus, bld and bld+ both refer to the bald gene.

  1. Homologous chromosome pairs are indicated with a ‘/’ (slash) symbol.
  2. Genes on nonhomologous chromosomes are separated by a ‘;’ (semicolon) symbol.
  3. Linked loci (loci that are on the same chromosome) are listed together on the same side of the slash.
If you forgot the rules, check out "linked genes".