Alternative methods for predicting germ cell-specific expression from gonadal microarray studies. Precision-recall curves were plotted to evaluate the performance of alternative methods. A. Gonadal expression levels. The average of gonadal expression across prophase was computed for each training gene. Genes were sorted in descending order of log2 expression, and precision and recall were calculated with a log2 expression decrement of 2. B. Gonadal expression correlation. Pearson correlation of gonadal expression across prophase was calculated for each training gene pair. Gene pairs of the same type (both germ cell genes or non-germ cell genes) served as the positive correlation examples; gene pairs of different types (one germ cell gene and one non-germ cell gene) served as the negative correlation examples. Training gene pairs were sorted in descending order of correlation coefficient, and precision and recall were calculated with a coefficient decrement of 0.002.