Chromosomal abnormalities are changes in the number or structure of chromosomes, which are the thread-like structures in cells that carry genetic information. These abnormalities can occur during cell division and may lead to various health issues, including developmental disorders and increased risk of certain diseases. There are two main types of chromosomal abnormalities: numerical and structural. Numerical abnormalities involve an abnormal number of chromosomes, such as in Down syndrome, where there is an extra copy of chromosome 21. Structural abnormalities involve changes in the chromosome's structure, such as deletions, duplications, or translocations, which can disrupt normal gene function.