16.5: Three-Letter Symbols
selected template will load here
This action is not available.
It’s perfectly acceptable to use a single letter or even two letters. Sometimes, though, multiple traits spelled with the same first letter can get confusing. Using three letters for a gene symbol can make it easier to remember what the letters stand for. In fact, for some model systems those who study them adopt a defined nomenclature system. A plant often used for genetic studies, called Arabidopsis thaliana , has a three‐letter code ( https://www.arabidopsis.org/portals/nomenclature/namerule.jsp ).
Just as we saw for the one‐letter symbols, the dominant allele has the first letter capitalized and the last two letters are lower-case. Recessive alleles are all lower-case. With three letters, you can make gene names that are easier to keep track of. For example, you might see a fly with an extra set of wings. Instead of calling it “ w ” for “wings” (which is a poor choice because it doesn’t represent the mutant phenotype), you can instead call it “ exw ” for “ ex tra w ings”. Then, when you see it, you can sound out the abbreviation and remember that it stands for the mutation. If the wild-type allele for this is dominant, then you would write that one “ Exw ”. The first letter indicates that it is the dominant allele. What you can’t tell just from these examples is that wild-type allele is dominant! Appendix 2 will go into an extension of this system so you can add that information to the gene symbol. Hint : remember in Section 3.2 that the “+” superscript indicates the wild‐type allele.
1.4 Three Letter System