Chromosomal mutation may result either due to changes in the chromosome structure or due to an abnormal number of chromosomes. These mutations may be caused by several different factors including but not limited to: 

• Mistakes during chromosome division or fertilization 
• Mistakes during crossing over 
• Irregularities in nuclear 
• Loss of portions of chromosomes during anaphase and/or nuclei reorganization
• Digestion of portion of chromosomes by nucleases
• Irregularities during meiosis
• Duplication of a portion or the entire chromosome during division 
• Exposure to mutagens such as chemical molecules or radiation