Chromosomal abnormalities occur when there is a change in the number or structure of chromosomes in a person's cells. Humans typically have 46 chromosomes, arranged in 23 pairs. When there are extra chromosomes, missing chromosomes, or structural changes, it can lead to various health issues or developmental disorders. For example, Down syndrome is caused by an extra copy of chromosome 21. These abnormalities can happen during cell division, often due to errors in the process. Some chromosomal abnormalities are inherited from parents, while others occur spontaneously. Early detection through genetic testing can help manage and understand the implications of these conditions, improving outcomes for affected individuals.