Genetic DeÞnition and Sequence Analysis of

High-precision genetic mapping was used to deÞne the regions that contain cen-tromere functions on each natural chromosome in Arabidopsis thaliana. These regions exhibited dramatic recombinational repression and contained complex DNA surrounding large arrays of 180Ðbase pair repeats. Unexpectedly, the DNA within the centromeres was not merely structural but also encoded several ex-pressed genes. The regions ßanking the centromeres were densely populated by repetitive elements yet experienced normal levels of recombination. The geneti-cally deÞned centromeres were well conserved among Arabidopsis ecotypes but displayed limited sequence homology between different chromosomes, excluding repetitive DNA. This investigation provides a platform for dissecting the role of individual sequences in centromeres in higher eukaryotes. Centromeres mediate chromosome segrega-tion during mitosis and meiosis by nucleating kinetochore formation, providing a target for spindle attachment, and maintaining siste