ABSTRACT
Radiation biologists have a long history of working with unconventional models, using whatever was most accessible and most appropriate for their research. These have included virus, bacteria, slime molds, amoeba, the yeasts Saccharomyces and Neurospora, eggs of the parasitic wasp Habrobracon, the fruit fly Drosophila melanogaster, the unicellular alga Acetabularia, the ciliates Tetrahymena and Paramecium, fern spores, and frogs’ eggs. Molecular biologists and geneticists working with mammalian systems
have turned to lower organisms, particularly lower eukaryotes, for specific reasons. Eukaryotic cells have typically 3-30 times as many genes as prokaryotes, and often thousands of times more noncoding DNA allowing for the complex replication of gene expression required for the construction of multicellular organisms. Some eukaryotes are unicellular, however, among them the yeast Saccharomyces cerevisiae one of the simplest model organisms for eukaryotic cell biology, revealing the molecular basis of conserved fundamental processes such as the cell division cycle. A small number of other organisms have been chosen as primary models for multicellular plants and animals and the sequencing of their entire genomes has opened the way to systematic and comprehensive analysis of gene functions, gene regulation, and genetic diversity. As a result of gene duplications during vertebrate evolution, vertebrate genomes contain multiple closely related homologues of most genes. This genetic redundancy has allowed diversification and specialization of genes for new purposes, but it also makes gene functions harder to decipher. There is less genetic redundancy in, for instance, the nematode Caenorhabditis elegans and the fruit fly Drosophila melanogaster which have played a key role in revealing the universal genetic mechanisms of animal development.
