A chromatin is a strand of DNA wound tightly around proteins called histones whereas a gene is a segment of DNA strand that tells the cell to make a specific protein. There are two basic types of chromatin. Euchromatin and heterochromatin. Euchromatin is the genetically active type of chromatin involved in transcribing DNA to produce protein. It is more diffuse than heterochromatin. A gene is the basic physical and functional unit of heredity. Genes, which are made up of DNA, acts as instructions to make proteins. In humans, genes vary in size from a few hundred bases to more than 2 million bases. It is estimated that humans have between 20,000 and 25,000 genes.