All organisms have two copies of each gene for a given trait. They get one copy from each parent. A gene is the portion of a(n) chromosome that controls a particular inherited trait. Information needed for cells to function are contained in genes. Genes are sections of a long, complex molecule called DNA. The shape resembles a spiral staircase. Its steps are made of chemical compounds called bases. They fit together like the pieces in a(n) puzzle. The order in which the base pairs appear allows for a large number of combinations. DNA contains the codes that tell each cell how to operate.