The development of an adult organism starts with a fertilized egg that differentiates into hundreds of specialized cell types comprising tissues and organs. How these cell fate changes happen is a subject of research interest. All cells contain the same genetic information, and development therefore involves the selective regulation of genes contained in the DNA. The proteins that turn these genes on or off are called transcription factors. Similar mechanisms operate when a stem cell in the adult body, such as the blood stem cell, specializes into cell types needed for different functions. To ensure correct gene regulation, additional kinds of proteins are required, such as enzymes that modify proteins that wrap around the DNA or even the DNA itself, thus fine tuning this complex process. Interestingly, alterations of these proteins due to mutations leads to aberrant gene regulation and often results in the formation of cancer.