Final answer:
A trisomy is a genetic condition where an individual has three copies of a particular chromosome instead of two, often resulting in developmental issues and medical conditions such as Down Syndrome, which is caused by an extra chromosome 21.
Step-by-step explanation:
A trisomy refers to a chromosomal disorder where an individual has three copies of a particular chromosome instead of the usual two. The presence of an extra chromosome can cause a variety of developmental and medical issues due to an imbalance in gene dosage.
For instance, the most well-known trisomy is Trisomy 21, also known as Down Syndrome, where individuals have an extra copy of chromosome 21.
This condition is characterized by distinct facial features, developmental delays, and it becomes more likely to occur in children born to older mothers due to an increased risk of chromosomal nondisjunction during meiosis as women age.
To diagnose a trisomy, a karyotype analysis is conducted, where metaphase chromosomes from a cell sample are photographed and examined for any discrepancies in chromosome number or structure. This analysis can reveal trisomies like Trisomy 8, 9, 12, 13, 16, 18, and 21, among others.
While some trisomies result in non-viable pregnancies, certain conditions like Down Syndrome can lead to a viable birth and a lifespan ranging from a few weeks to many years, depending on the severity and medical care provided.