|Uterus of rat with fetus | Stereomicroscope SMZ171 | Moticam 10|
Laboratory rats have bicornuate uteri and weigh between 200 and 400 g. There are numerous different "strains" with slightly different gestational features. A commonly
used animal is the Wistar rat; it is white in color. Another important strain is the Sprague Dawley rat, but many more well-known strains are also employed for research purposes.
Rat embryos do have the advantage of being much larger than mouse embryos and are easy to breed. Both rodents, rat and mouse, with whom humans had a common ancestor 75 million years ago, roughly possess as many genes as we have: 25 to 30 000. But deep down the rat seems to be the most like us: 90 percent of its genes have a human counterpart. For this analyses, the researchers have used the brown rat, or sewer rat.