This past spring/summer I had the opportunity to give talks at both the Drosophila Research Conference in San Diego, CA and the Evolution Conference in Portland, OR about my research on reproductive isolation and sexual selection in Drosophila pseudoobscura. During the Drosophila conference I was able to meet Steve Schaeffer (Penn State) who invited me down to State College, PA to learn his technique for polytenes.
Polytene chromosomes are formed in the salivary gland of Drosophila larvae when cells undergo repeated rounds of DNA replication without mitosis creating large cells. The DNA of these cells can be stained to show specific banding patterns that can identify chromosomes, specific genomic regions, and inversion karyotypes. I had been wanting to learn how to prepare polytenes to help identify inversion status of my wild-collected D. pseudoobscura collections.
Steve was a great host and I had a fun visit working on getting nice preps throughout the day. Steve has perfected his technique through his career and it has enabled him to make key insights about local adaptation maintaining inversions across the range of D. pseudoobscura. To be able to distinguish banding patterns the chromosomes cannot be flattened too much or they become distorted, which was quite difficult for me as a beginer. Below is a preparation Steven made that identified a line from Lamoille Canyon, NV that was polymorphic for a inversion.