What is the definition of trisomy?

Trisomy is defined as the presence of three copies of a particular chromosome instead of the usual two. This genetic condition occurs when there is an error during cell division, specifically during meiosis or mitosis, leading to an extra chromosome being included in the gamete or zygote. As a result, the individual has a total of three copies of that chromosome.

For example, Down syndrome is a well-known condition caused by trisomy 21, where there are three copies of chromosome 21. This extra genetic material can lead to various developmental and health issues associated with the syndrome.

Understanding trisomy is crucial in the study of genetics and chromosomal abnormalities, as it highlights how variations in chromosome numbers can significantly impact an organism's phenotype and overall health.