I have been meaning to post about another big Heliconius paper that came out earlier this year which made a major advance in our knowledge of the genes underlying Heliconius wing patterning. We have known for some time now, from work led by Simon Baxter in my lab, that a narrow genomic interval is responsible for controlling red wing patterns in both the co-mimics H. melpomene and H. erato. In a paper earlier this year, Bob Reed’s lab made a major advance on this by showing that the optix gene is expressed in a pattern completely correlated with red wing patterns in the developing pupa. This was first uncovered by Riccardo Papa using a microarray experiment, and then elegantly confirmed by Arnaud Martin with in situ hybridisation. Optix is a transcription factor, a gene that regulates the expression of other genes. There are no coding differences between optix sequences in different populations, which shows that regulatory changes underlie the difference in expression.