Many Paths to the Top of the Mountain

Abstract

Centromeres have many properties that distinguish them from noncentromeric regions of the genome, and a few of these, which are both important and experimentally accessible, have been used as definitions to identify the centromere. These include delineation of a region by tetrad analysis in yeast and Arabidopsis (see below), stable inheritance through mitosis and/or meiosis of structures introduced as naked DNA (yeasts) or arising from rearrangement of an existing chromosome in vivo (Drosophila, human), and centromere protein binding (human). These different definitions will not necessarily identify the same region of DNA or require the same proteins: for example, meiotic requirements may differ from mitotic requirements, and de novo centromere formation is usually an artificial process that may have different requirements from maintenance of an existing centromere. Some workers emphasize the distinction between the centromere (the underlying chromatin) and the kinetochore (the external protein structure), but such a distinction is not easy to make in all species.