Laboratory mice are specialized strains of house mice, with scientists carefully controlling the traits they exhibit through prescribed breeding and genetic engineering. Since strains of laboratory mice are homogenous and standardized, genetic variability can be removed as a possible complicating factor, making experimental results more reliable. Mice have been utilized extensively to research various human disorders, such as cancer, blindness, multiple sclerosis, and seizures. Similarly beneficial for basic research purposes, mice have helped scientists acquire a better understanding of how vertebrate embryos develop and how modifications of the prenatal environment can affect a fetus.