University of Michigan evolutionary biologists Ben-Yang Liao and Associate Professor Jianzhi Zhang said their findings have serious implications for the use of mouse models in studying human disease.

"Everyone assumes deletion of the same gene in the mouse and in humans produces the same phenotype," said Zhang. "Our results show that may not always be the case."

Zhang and graduate student Liao focused their study on 120 so-called essential genes which, through their effects on survival or fertility, are necessary for organisms to reach sexual maturity and reproduce.

"To our surprise, 22 percent of the 120 human essential genes are non-essential in the mouse," Zhang said.

"If our sample is unbiased, our results will have some important implications," he said, noting people draw inferences about gene function by using information from other organisms. "We need to be careful doing this because … genes may have different functions or different importance in different species."

The study appears in the Proceedings of the National Academy of Sciences.