Butterfly wing patterns have been a subject ofscientific research for well over a century. More recently they have become a prominent system for the study ofthe developmental and genetic processes which underlie morphological variation and evolution. The neotropical butterfly genus Helicon ius is at the centre ofthis research. In this genus, past research has revealed that the colour patterns ofthese butterflies, which are selected for maintenance ofmimicry (Mallet and Barton, 1989) and by mate preference (Jiggins et aI, 2001), are controlled by relatively few loci (Sheppard et aI, 1985; Naisbit et aI, 2003), often referred to as 'switch' genes. More recently, research has shown that the genes controlling convergent pattern elements are in homologous genetic positions even in widely diverged Heliconius species (Kronforst et aI, 2006b; Joron et al, 2006). In this thesis a chromosome walk at the genomic location ofone ofthese patterning genes, Yb, has been carried out in He/icon ius melpomene, utilising a Bacterial Artificial Chromosome (BAC) library. Several candidate genes for this locus have been identified, and additionally markers generated in the Yb walk have been used to facilitate walks at homologous genomic locations in H. erato (the distantly related co-mimic of H. melpomene) and H. numata (the divergently patterned sister species ofH. melpomene). I have also screened the H. melpomene BAC library with markers designed to other patterning genes, and identified clones, confinned and selected for sequencing. This data will prove useful for future comparative analyses and in the future help detennine the likely interactions between the switch genes and the pigmentation and wing development pathways. Finally, the entire BAC library was end-sequenced (by the Wellcome Trust Sanger Centre), and these data were analysed and infonnatiori on the H. melpomene genome extracted. Overall, this sequence gives us 21.4 Megabases ofnovelH. melpomene sequence, which equates to just over 7% ofthe genome. These data have allowed the identification ofareas potentially containing novel repeats, and will also facilitate further chromosome walks at regions ofinterest in the future.