Chromosome units are made up of genes, which are the basic unit of heredity. Genes are composed of DNA and are responsible for the transmission of traits from one generation to the next. Chromosomes are structures within cells that contain genetic material in the form of genes. Each chromosome is made up of many genes, which are the functional units of heredity. Chromosomes are found in the nucleus of every cell in the body and are responsible for the transmission of genetic information from one generation to the next.