12 Drosophila Telomeres: Another Way to End It All

Abstract

The idea that the end of a chromosome forms “a permanent distinctive organelle, the ‘telomere’” (Muller 1941) was initially based on studies with Drosophila. Reviewing the results of a decade of studies by Drosophila geneticists on chromosome breakage and rearrangements, Muller (1938) concluded that chromosome ends acted as caps to prevent the fusion of intact ends with broken ends, because such fusions were never seen. In addition, terminal deletions were seen rarely, if at all (see Gall, this volume). Since terminal deletions would require only one break and no rejoining, they might be expected to be relatively frequent. Surprisingly, very few were found, and those were usually reclassified as translocations when analyses of the giant polytene chromosomes revealed small amounts of new material on the broken end (Muller 1941; Roberts 1976). Muller concluded that a broken end that failed to find and fuse with another broken end would lead to the loss of the broken (“atelomeric”) chromosome and, therefore, the loss of the cell. This evidence that chromosome ends were essential “caps” led Muller to name the ends telomeres. Genetic analysis combined with cytological analysis of polytene chromosomes provided strong evidence for telomeres in Drosophila. Cytogenetic analyses cannot be carried out as easily on most other organisms, but evidence available from both plants and animals supports the idea that telomeres of all eukaryotes are similar. The picture of the molecular structure of telomeres was originally derived from studies on protozoa and yeast but is also consistent with data derived from...