7.5, 0.7, 0.4, and 0.3 g of embryos at four different stages, respectively, were used to prepare chromatin for immunoprecipitation following the CsCl2 gradient ultracentrifugation protocol as previously described (Harrison et al., 2011).The chromatin obtained was fragmented to sizes ranging from 100 to 300 bp using a Bioruptor (Diagenode, Inc.) for a total processing time of 140 min (15 s on, 45 s off), with power setting at "H". Prior to carrying out chromatin immunoprecipitation, we mixed the chromatin from each sample with a roughly equivalent amount of chromatin isolated from stage 5 (mitotic cycle 14) D. pseudoobscura embryos, and used about 2 µg of total chromatin (1 µg each of the D. melanogaster and D. pseudoobscura chromatin) for each chromatin immunoprecipitation. The chromatin immunoprecipitation reactions were carried out as described previously (Harrison et al., 2011) with 0.5 ug anti-H4K5ac (Millipore, 07-327), 0.5 ug anti-H3K4me3 (Abcam, ab8580), 0.5 ug anti-H3K27ac (Abcam, ab4729), 1 ug anti-H3 (Abcam, ab1791), 0.75 ug anti-H3K4me1 (Abcam, ab8895), 0.75 ug anti-H4K8ac (Abcam, ab15823), 1.5 ul anti-H3K9ac (Activemotif, 39138), 0.75 ug anti-H3K18ac (Abcam, ab1191), 3 ug anti-H3K27me3 (Millipore, 07-449), or 0.75 ug anti-H3K36me3 (Abcam, ab9050). The sequencing libraries were prepared from the ChIP and Input DNA samples using the Illumina TruSeq DNA Sample Preparation kit following the manufacturer's instructions, and DNA was subjected to ultra-high-throughput sequencing on Illumina HiSeq 2000 DNA sequencers. The libraries were combined into pools, with each containing 6-8 libraries with different index and at similar concentrations, and each library pool was sequenced (100 bp single-end read) in a single lane in a flow cell.