Chromosomal aberration refers to any change in the normal structure or number of chromosomes in a cell. These changes can occur during cell division and may result in missing, extra, or irregularly shaped chromosomes. Such alterations can lead to various genetic disorders and diseases, including some types of cancer. There are two main types of chromosomal aberrations: numerical and structural. Numerical aberrations involve changes in the total number of chromosomes, such as Down syndrome, which is caused by an extra copy of chromosome 21. Structural aberrations involve alterations in the chromosome's structure, such as deletions, duplications, or translocations, which can disrupt gene function.