The two main functions of the genetic material in a cell, also known as DNA, are gene expression and replication. DNA accomplishes gene expression by providing the instructions necessary for cell machinery to make proteins. Replication occurs when the DNA makes a copy of itself for incorporation into a new cell.
Sections of DNA that code for proteins are called genes. However, the majority of the genetic code does not actually code for proteins. While the non-coding portions of DNA were once referred to as "junk DNA" and thought to have no actual function, those regions are now thought to play a role in the regulation of gene expression.
Replication of the genetic material takes place through two processes, mitosis and meiosis. In mitosis, the cell uses DNA as a template to build a second copy of DNA in the nucleus. The nucleus then splits, along with the whole cell, and two daughter cells are formed, each with its own identical copy of DNA. In meiosis, after the complete DNA copy is made, only half of the DNA goes into each of four progeny cells. These cells are gametes. Each gamete can combine with another gamete during sexual reproduction to form a new organism containing half of the genetic material from each parent.