Marker enzymes are specific enzymes produced by cell organelles.
Complex organisms, such as animals and plants, are composed of millions of cells. Even though they each derived from a single fertilized cell and contain a complete copy of that organisms DNA (genome) their bodies are made up of different specialized tissues, such as skin, muscle, nerves, and blood. Different tissues express specific subsets of the total genome, activating some genetic pathways and leaving others inactive.
The basic body cells all contain the same set of organelles, the specialized areas within a cell that carry out metabolic functions. The development of these internal compartments allow for such intense, and wildly successful, differentiation of tissues, organs, and body plans.