Chromosomal duplication is a genetic process where a segment of DNA is copied, resulting in two identical copies of that segment. This can occur naturally during cell division, specifically in the S phase of the cell cycle, when DNA is replicated. Duplications can also happen due to errors in DNA replication or external factors like radiation. These duplications can lead to changes in an organism's traits and may contribute to evolution by providing additional genetic material for mutations. However, they can also cause genetic disorders if the duplicated genes disrupt normal cellular functions or regulatory mechanisms.