Qualitative and quantitative genetic studies of Arabidopsis thaliana.

G ENETIC research involving Arabidopsis thaliana dates back to the 1940s. A renewed interest has developed recently, however, due to recognition of the unique genomic properties of Arabidopsis, which make it an ideal system for molecular studies of flowering plants. This interest has increased to such a point that the international community of Arabidopsis geneticists organized a formal Arabidopsis thaliana Genome Research Project (MEYEROWITZ et al. 1990). Their overall goal is “to understand the physiology, biochemistry, and growth and developmental processes of a flowering plant at the molecular level, using Arabidopsis as an experimental model system.” The plan for this project predicts, with some assurance, that “recent progress in the area of genome mapping and of sequencing of specific genes amply demonstrate that Arabidopsis will be as useful to plant biology, and possibly to higher eukaryotes, as E. coli has been to microbiology in particular and to biology in general.” This is heady stuff to be focused on a small, useless ( i .e . , noncommercial) plant, but it indicates that many plant biologists worldwide have confidence that Arabidopsis is becoming the system of choice for flowering plants. There have been many reviews of Arabidopsis genetic research over the years, including eight since 1985. Hence a similar review will not be presented but rather a different perspective will be given, with a different orientation of past work and future prognoses. Here, Arabidopsis research is partitioned into a dichotomy based on the complexity of the genetic systems. The two categories are qualitative and guantitatzue systems. The qualitative studies deal with genes of sufficiently large effect to be manipulated individually. The quantitative genetic studies deal with variables controlled by genes at many loci which are, characteristically, strongly influenced by environmental fluctuations. Such a classification is somewhat arbitrary, and under certain conditions one system may