Characteristics Of Organisms Used For Genetic Studies

o General Features of an Organism Used for Genetic Studies

o good genetic background
o easy to grow
o controlled matings possible
o can be genetically engineered
o funding available
o Viruses

o easily grown in culture
o rapid generation time
o encode only a few the proteins, which permit a detailed analysis of well-defined system
o some viruses have control mechanisms found in eukaryotic species
o can be genetically engineered
o lack organized chromosome
o not all genetic features can be extrapolated to other organisms

o Escherichia coli

o easily grown in culture
o rapid generation time
o many mutants available
o many genes involved
o life cycle very well defined
o relatively simple to generate new mutants
o can be genetically engineered
o contain a rudimentary chromosome
o not all genetic features can be extrapolated to higher organisms

o Human

o intense public interest and funding available
o relatively well-mapped for most eukaryotic species
o many diseases (mutant phenotypes) understood clinically
o well-defined cytogenetic system
o long generation time
o many traits can only be studied in cell culture
o cannot make controlled crosses
o cannot be genetically engineered

o Drosophila

o short generation time for a eukaryotic organisms (two weeks)
o availability of many mutants controlling specific phenotypes
o large chromosomes with well-defined cytogenetic system
o survives well in the lab and matings are easily performed
o currently, the best organism to study developmental genetics
o transposable elements can be manipulated to clone genes
o can be genetically engineered

o Maize

o best mapped plant species
o many mutants are available that control seed traits
o well-defined cytogenetic system
o transposable elements well understood and can be used to clone genes
o matings tedious, but produce many (hundreds) of progeny
o only three generations per year
o cannot be easily genetically engineered
o not well funded

o Arabidopsis thaliana

o small genome with little repetitive DNA
o short generation time (six weeks)
o many mutants rapidly becoming available
o matings tedious, but produce many (thousands) of progeny
o currently, an intensely investigated organisms; the Drosophila of plant species
o can be easily genetically engineered
Although these species have been studied intensely, these are by no means the only species analyzed for genetic studies. Mouse has been used for many genetic studies because it is a mammal that is a relatively good model for human gene expression. A good example is the globin genes, protein that carry oxygen in blood cells. The genetic and molecular organization of the mouse and human genes are quite similar: they have the same number of exons and have the introns located at the same amino acid residue in the transcript. Furthermore, the order of the multigene family is conserved. Yeast has also been well studied. Although this species is a good model system, this is not the reason that it was first investigated. The primary reason was because of its role in brewing.

In addition many plant species have relatively well-defined genetic systems. Tomato, next to corn, is the best mapped plant species. Tobacco has become a valuable tool to study plant molecular genetics because of the ease in which it can be genetically engineered at the whole plant level. This permits the molecular analysis of many genes in the functioning organism, rather than in a cellular condition as is the case with animal systems.

The genetic systems of many other plant species have been analyzed by plant breeders who need to understand how specific traits are genetically controlled. This information is important so that the traits can be successfully manipulated in a breeding program. This ability to manipulate crop plants is not a recent discovery. That native Americans were aware of the concept of heredity is evidenced by their deliberate attempts to maintain specific lines of their crops that were adapted to or superior in their environment.

Model Organism Research
Most mapping and sequencing technologies were developed from studies of nonhuman genomes, notably those of the bacterium Escherichia coli, the yeast Saccharomyces cerevisiae, the fruit fly Drosophila melanogaster, the roundworm Caenorhabditis elegans, and the laboratory mouse Mus musculus. These simpler systems provide excellent models for developing and testing the procedures needed for studying the much more complex