In diploid organisms, chromosomes occur in matching pairs, with the exception of the sex chromosomes. Not all organisms are diploid; for example, bacteria have only one circular chromosome, and some insects may have an odd number of chromosomes. Every human somatic cell (excluding egg or sperm cells) has forty-six chromosomes—twentytwo somatic chromosome pairs and one sex chromosome pair. The somatic chromosome pairs, called homologous chromosomes, carry the same sequence of genes for the same inherited characteristics.