This study focuses on funding causes of individual differences in how the brain works. In many animals, short days during the winter cause individuals to become infertile until better conditions in spring. Two strains of mice have been produced that differ strongly in this feature. One strain becomes infertile in short day lengths, and the other does not. These strains will be used to compare brain chemicals and cells in the brain that cause these differences in how the brain controls fertility. Differences will be further tested in a wild population of mice. The goal is to understand a major question in animal biology - how do cells and brain chemicals cause individual differences in how the brain functions, and specifically how do they control fertility and infertility. More broadly, understanding individual differences in the brain will contribute to understanding variation in animal behavior and variable responses to medical treatment. In education, undergraduate students need better mentoring program, will provide an undergraduate course on research, ethics, and careers in science, will bring research into classroom, and will train undergraduates in research methods by intensive involvement in actual research.