Scientists have created a new kind of mouse by replacing the genetic material in the mitochondria of one species with that from another in a gene-swapping exercise necessary if doctors are to understand several currently untreatable human diseases.

Mitochondrial medicine — how specific mitochondrial mutations and deficiencies lead to disease — deals with trouble with the cell’s powerhouse, the mitochondrion, which affects many diseases that become more common as people age, from infertility and diabetes to cancer, Alzheimer’s and Parkinson’s diseases.

University of Rochester Medical Center press release