Model organisms are species that are extensively studied to understand particular biological phenomena, with the expectation that discoveries made in the organism model will provide insight into the workings of other organisms. Genetics model organisms include E. coli, yeast, C. elegans, Drosophila, corn, Arabidopsis and mouse.
Forward Genetics for dissecting gene function
Forward genetics means when a phenotype is observed, a gene locus is correlated to that phenotype, the gene is then isolated and studied at molecular level. It includes a few standard steps: identification of the mutant, mapping the mutant, mutant allele tagging and gene isolation.
Reverse genetics for dissecting gene function
In reverse genetics, a gene sequence is known but its function is unknown. The gene is “knocked out” in the genome or, its function is inhibited transcriptionally (namely by siRNA), the phenotype is observed. This mainly involves two strategies: homologous recombination-based gene knockout and siRNA-based gene silencing.
Gene knockout in model organisms
Gene knockout in C. elegans usually use chemical mutagenesis method, which can be done in large scale. Gene knock out is a powerful tool in biomedical science, especially the mouse model of human diseases. For knockout mouse generation, a homologous recombination-based knock-out construct is made and introduced into mouse ES cells, the recombinant are screened and selected, the ES cell were then introduced back into a developing mouse embryo. Thus a chimeric mouse is obtained. This mouse is crossed with a wild-type mouse, some of the progeny will have the knock-out allele, these are called heterozygous. Homozygous can be obtained using cross among the heterozygous siblings.