Three mice, two blind.

Abstract

In a closed colony of approximately one million mice which had been rigidly pedigreed (brother to sister) from a few original mice, three unusual mice have appeared. These three have obviously deviated from what would be expected according to the accepted laws of inbreeding geneity. Thus three unexpected incidences of increased variability have occurred three times in addition to the occasional appearance of new mutations (approximately one in 26,000 mice). The first mouse developed a sudden increase in susceptibility to spontaneous tumors of mammary origin. She became the mother of the well-known C family used extensively in cancer research. The second mouse clearly exhibited, among clear-cut altered biological characteristics, several somatic mutations, thus indicating an unstable genetic condition. The third mouse developed a highly significant capacity to regress and eliminate spontaneous tumor tissue. The conclusion is reached that unstable biological states arise occasionally during the process of inbreeding.