How Drosophila melanogaster genes are named

Drosophila melanogaster is known for its interesting genes, with legendary examples like hamlet, cheapdate, dreadlocks, and swiss cheese, among hundreds of others. But these names aren’t just for fun and games. In fact, one of the most important things you’ll learn while working with D. melanogaster is its rules for gene naming.

The basics of Drosophila melanogaster gene naming

First, the basics. D. melanogaster genes are always written in lowercase italics, and their corresponding proteins in Sentence case, Non-italics. Like this 👇

Gene: dreadlocks
Protein: Dreadlocks

Drosophila melanogaster gene names
Example gene names and their chromosomal locations. Image adapted from “Engineering the Fruit Fly Genome.”

Drosophila melanogaster genes are typically named after their mutant phenotype

This idea sounds complicated but it’s actually more simple and intuitive than you might expect. Let’s start with the classic example of the white gene, which plays a key role in the fly’s normal red eye coloration. “But why would a gene named white help create red eyes?” you might be asking. Well, let’s see.

The tale of the white gene begins in a 1910 study by Thomas Hunt Morgan, a famous pioneer in Drosophila research. In this paper, Morgan discovered a white-eyed male fly among his normal, red-eyed stock. He speculated that the white-eyed male carried a “factor” for white eyes, which he called “W” (Remember this is decades before we understood that DNA is the genetic material, so the “factor” he described was somewhat abstract in his mind).

Drosophila melanogaster white eye mutation
White-eyed mutant fly, and normal (wild-type) red-eyed fly. Image adapted from Thomas Hunt Morgan article on NobelPrize.org

What Morgan didn’t fully grasp at the time – since he wasn’t aware of the biochemical pathways that produce Drosophila’s red eyes – is that this white-eyed male carried a mutation in the white gene, which encodes a protein essential for transporting red and brown pigments into the cells of the developing eye1. Thus in the absence of a functional White transporter protein, no colorful pigments made it into the eye, which remained a plain empty white color.

Mutagenesis (i.e. the process of creating mutations in an organism) is a powerful tool because we can use it to infer the normal function of a gene, by looking at what happens when that gene is mutated. In the example above, Morgan observed a mutant fly with white eyes. Therefore, he named the affected gene (or “factor”) “white.”

In today’s naming convention, a normal version (i.e. allele) of the white gene would be called white+, and a null allele (i.e. a totally non-functional version of the gene) would be called white. Every unique white mutation catalogued would get a different number: white1, white2, and so on. Flybase is a great resource for looking up all the mutant alleles of your gene of interest; there can be dozens of mutant alleles of a single gene, producing a range of phenotypes.

Drosophila melanogaster eye color mutations
Some of the many D. melanogaster eye-color mutants that have been discovered since the original white mutant strain. Each of these genes represents a different component of the eye coloration pathway. Image source.

The process described above is fairly common practice in Drosophila melanogaster research. It takes, as a starting point, a particular mutant phenotype and then works to identify the causative mutant gene; this is what explains the somewhat backwards convention of naming a gene after its mutant phenotype.


If you enjoyed this summary of how Drosophila genes are named, check out my post All about Drosophila melanogaster chromosomes.


References

  1. Grant P, Maga T, Loshakov A, et al. An Eye on Trafficking Genes: Identification of Four Eye Color Mutations in Drosophila. G3 (Bethesda). 2016;6(10):3185-3196. Published 2016 Oct 13. doi:10.1534/g3.116.032508

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