Gene—Milk Agent Relationship in Mammary-Tumor Development

Abstract

In the mouse it has been established that genetic factors influence the development of mammary tumors. In this experiment 14 high mammary-tumor strain C3H (containing 100% susceptible strain chromatin and milk agent) females were mated with low mammary-tumor strain C57 (100% resistant strain chromatin and no milk agent) black males. 52 of the 82 resulting hybrid female offsprings were backcrossed (the remaining 32 were retained as virgins) to males of each parent strain. Weekly examinations for tumors were made. Tumorous and nontumorous mice were necropsied and histologic tumor diagnosis made. The results show that susceptible-strain chromatin transmitted the agent more effectively to the test females than did resistant strain backcrossed females with an average of 25% susceptible strain chromatin although both backcross groups had received identical milk agent and other maternal influences. Segregation of more than 1 pair of genes influenced the propagation and transmission of the agent. 2 sets of genetic factors aside from the hormonal kind were found to influence mammary tumor development. One set determines the susceptibility of the mammary tissue cell to the hormonal and milk-agent stimuli and the other the propagation of the milk agent. All tumorous backcross females were able to transmit the agent while only a part of the nontumorous females transmitted the agent. These 2 sets had 1 or more factors in common as evidenced by the fact that the nontumorous backcross females which did transmit the agent transmitted it less effectively than did the tumorous backcross females. A comparison of tumor incidences of 2 groups of backcross females with uniform extrachromosomal factors revealed that genetic factors alone could determine the chance of a females developing mammary tumor.