There are about 75 different types of cells in the human brain. What makes them all different? Researchers at Baylor College of Medicine have developed a new set of computational tools to help answer this question. Although different cell types from the same organism carry the same DNA, they look and function differently because a different set of genes is active or inactive in each. Cells switch genes on or off by using epigenetic mechanisms, such as DNA methylation, which involves tagging genes with methyl chemical groups.