trisómískur

Trisómískur refers to a genetic condition where an individual has three copies of a particular chromosome instead of the usual two. This is a type of aneuploidy, which is a condition characterized by an abnormal number of chromosomes. The most common and well-known form of trisomy in humans is Down syndrome, also known as trisomy 21, where there are three copies of chromosome 21.

Other forms of trisomy exist, though they are often less common or result in more severe developmental issues. For instance, trisomy 18 (Edwards syndrome) and trisomy 13 (Patau syndrome) are also known chromosomal abnormalities that lead to significant health challenges and are typically associated with a shorter lifespan. The extra genetic material from the third chromosome disrupts the normal course of development, leading to a range of physical and cognitive characteristics that vary depending on which chromosome is affected and to what extent.

The occurrence of trisomy is usually due to an error during cell division, specifically during the formation of egg or sperm cells (meiosis). This error, called nondisjunction, causes the chromosomes to fail to separate properly. While the exact reasons for nondisjunction are not fully understood, advanced maternal age is a known risk factor for some trisomies. Genetic counseling and prenatal diagnostic tests can help assess the risk and confirm the presence of trisomy.