Single-nucleotide changes in the same genes but in different positions in the coding sequence might do nothing harmful at all. Add them all together, and they can make quite an impact, as evidenced by the huge range of metabolic, morphological, and behavioral differences we see among organisms. When researchers isolate human genes with unknown functions, they can create knockout mice with these genes and observe the results. Instead of creating merely the mouse equivalent of the human gene, researchers are able to reproduce and express actual human genes and their corresponding proteins in mice. This helps researchers understand health and disease by observing how genes work in cells.
Knockout mice have many benefits.
They not only allow researchers to determine gene function and understand diseases at the molecular level, but they also aid scientists in testing new drugs and devising novel therapies. Mice are genetically very similar to humans. They also reproduce rapidly, have short life spans, are inexpensive and easy to handle, and can be genetically manipulated at the molecular level. Numerous genomes have been completed including the fruitfly Drosophila melanogaster , the worm Caenorhabditis elegans , the bacterium Escherichia coli , the yeast Saccharomyces cerevisiae , the plant Arabidopsis thaliana , and several microbes. Genome size does not correlate with evolutionary status, nor is the number of genes proportionate with genome size.