On the Cover: Pollen grains from a quartet mutant of Arabidopsis, heterozygous for a pollen-specific, transgenic copy of GFP (green fluorescent protein), are shown. The quartet mutant makes it possible to examine all four products of individual meioses and to distinguish the expected 2:2 patterns (such as those shown here) from aberrant 3:1 or 4:0 patterns resulting from gene conversion, chromosome loss, or other genomic alterations. The Breakthrough Technologies article by Copenhaver et al. (pp. 7–15) describes other applications of the quartet mutation, including the construction of genetic maps, defining centromeres, investigating crossover interference, analyzing lethal mutant combinations, and screening gametophytic gene functions.