What genetic condition involves having one or more than the normal number of chromosomes?

Trisomy is a genetic condition characterized by the presence of an extra chromosome, resulting in three copies of a specific chromosome instead of the usual two. This anomaly occurs due to nondisjunction during cell division, where chromosomes fail to separate properly. As a result, individuals with trisomy have a total of 47 chromosomes instead of the normal 46, leading to various physical and developmental challenges, depending on which chromosome is affected. For instance, trisomy 21, also known as Down syndrome, is a well-known condition that arises from having an extra copy of chromosome 21.

Monosomy refers to the absence of one chromosome from a pair, disomy indicates having two copies of a single chromosome, and tetrasomy involves having four copies of a specific chromosome. While these terms describe different chromosomal anomalies, trisomy specifically denotes the presence of three chromosomes of one type, making it the correct response in this case.