lifespan of two years. They are widely considered to be the prime model of inherited human disease and share 99% of their genes with humans. With the advent Rodents have been employed in biomedical experimentation from the 1650s. Rodent studies up to the early 19th century were mainly physiological or toxicological. The first rodent behavioral study was carried out in 1822, a purely observational study, while quantitative rodent behavioral testing began in the late 19th century. Currently, rodents are commonly used in animal testing for physiological, Over… Mice are the most commonly used vertebrate species, popular because of their availability, size, low cost, ease of handling, and fast reproduction rate. Mice are quick to reach sexual maturity, as well as quick to gestate, where labs can have a new generation every three weeks as well as a relatively short lifespan of two years. They are widely considered to be the prime model of inherited human disease and share 99% of their genes with humans. With the advent of genetic engineering technology, genetically modified mice can be generated to order and can cost hundreds of dollars each. Transgenic animal production consists of injecting each construct into 300–350 eggs, typically representing three days' work. Twenty to fifty mice will normally be born from this number of injected eggs. These animals are screened for the presence of the transgene by a polymerase chain reaction genotyping assay. The number of transgenic animals typically varies from two to eight. Chimeric mouse production consists of injecting embryonic stem cells provided by the investigator into 150–175 blastocysts, representing three days of work. Thirty to fifty live mice are normally born from this number of…