Figure 4: A two-dimensional heat map illustrating a principal component analysis of the gene expression data from the 10 different segments of the mouse epididymis. Data sets are indicated as being very similar (white), somewhat different (yellow), and very different (red). The analysis shows that gene expression patterns in Segments 1, 2, 3, and 7 are unique unto themselves. Gene expression patterns in Segments 4, 5, and 6 are very similar, as are the patterns in Segments 8, 9, and 10. The illustration implies that the 10 segments of the epididymis form 6 sectors of unique function based on similarities of overall gene expression.