Chromosomes are rod-shaped structures made of DNA and proteins that store genetic information. They exist in cells only during cell division and unravel into chromatin between divisions. Prokaryotes have single circular chromosomes in the cytoplasm, while eukaryotes have multiple larger rod-shaped chromosomes in the nucleus. Humans have 46 chromosomes including 22 homologous chromosome pairs that determine traits and 2 sex chromosomes that determine gender. A karyotype is a picture of a cell's chromosomes arranged by homologous pairs to identify their number and structure.