Polysomy refers to the presence of an extra chromosome in an individual's genome. Some synonyms for polysomy include trisomy, tetrasomy, and pentasomy, which refer to the presence of three, four, or five copies of a chromosome, respectively. Other synonyms for polysomy include aneuploidy and chromosomal aberration, which more generally refer to any abnormality in the number or structure of chromosomes. Down syndrome, for example, is caused by trisomy 21, where an individual has three copies of chromosome 21 instead of the typical two. Chromosomal abnormalities like polysomy can lead to developmental disorders and other health conditions, making it important to identify and manage these conditions early on.