These images were generated using a fusion construct between the Drosophila melanogaster variant H2A.F/Z class histone, His2AvD, and the S65T version of the green fluorescent protein (GFP) of the jellyfish Aequorea victoria1., 2., 3.. The fusion protein produced by thisconstruct fluoresces brightly and labels interphase nuclei and condensed chromosomes from the late cleavage cycles through to adult cells. The images shown in Fig. 1 are: (a) a confocal section through nuclei of cleavage stage cycle 12 (bar, 5 μm), (b) a merged confocal image series of polytene chromosomes through a depth of approximately one-third of a salivary gland nucleus (bar, 5 μm), and (c,d) germline nurse cell nuclei and somatic follicle cell nuclei in developing oocytes viewed using epifluorescence microscopy (bars, 25 μm). Kanda et al. described a mammalian core histone–GFP fusion protein4, but the advantage of the fusion construct used here is that it is derived from a genomic fragment containing the His2AvD gene and is capable of rescuing His2AvD mutant lethality, confirming functionality3. This fusion protein can therefore be used as an in vivo marker for Drosophila chromosomes with confidence that cell function is not disrupted by expression of the construct. The H2A.F/Z class of variant histones are even more highly conserved than the core histones, so it is likely that the equivalent constructs in other organisms will be equally useful.