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Cover  The ability to create three-dimensional models of cellular structures has become an important part of cell biology. This is now a computer-assisted and sometimes computationally intensive endeavor. Such techniques include both confocal and deconvolution light microscopy, as well as reconstruction from electron micrographs of serially thin-sectioned material and electron tomography. A striking example of electron tomography appeared recently in the analysis of the Golgi complex (Ladinsky et al. [1999]. Golgi structure in three dimensions: functional insights from the normal rat kidney cell. J. Cell Biol. 144, 1135-1149). Of course, three-dimensional modeling began before the availability of the computer tools we enjoy today. One such study by Breck Byers and Loretta Goetsch (Byers, B., and Goetsch, L. [1975]. Electron microscopic observations of the meiotic karyotype of the diploid and tetraploid Saccharomyces cerevisiae. Proc. Natl. Acad. Sci. USA 72, 5056-5060) is featured on the cover. These authors took on the project of imaging yeast chromosomes in synaponemal complex (SC) during meiotic prophasethe one point in these cells' life cycle when the individual chromosomes can be seen in the electron microscope. An electron micrograph (top panel) shows short patches of the three-layered (two lateral elements and the central element) SC with dense nodules (N) indicated. This micrograph also contains a spindle pole body in the top right corner. The contours of the SC were traced from micrographs of serially sectioned nuclei onto clear plastic sheets. The tracings were aligned and bound together to allow viewing of the composite image that was rendered as a three-dimensional model of the SC in the given nucleus (bottom panel), effectively a karyotype. Remarkable and instructive in this study is the integration of this morphological data with available genetic and molecular data. Total SC length was divided into DNA content to determine a packing density, the number of chromosomes correlated with the available genetic data, and the distribution of chromosome lengths correlated with the distribution of map sizes for the various chromosomes. Furthermore, observations that have only recently been widely appreciated, such as the association of telomeres with nuclear envelopes, were reported in this decidely "low-tech" but powerful study of morphology in a well-characterized cell. The cover figure was reproduced with permission of the authors.Mark Winey