Klinefelter's Syndrome is caused by which chromosomal abnormality?

Klinefelter's Syndrome is indeed characterized by the presence of an extra X chromosome in males, leading to a karyotype typically represented as 47,XXY. This additional genetic material can disrupt normal sexual development and is associated with various symptoms, such as reduced testosterone levels, breast development (gynecomastia), and infertility.

The condition results from the nondisjunction of chromosomes during meiosis, where the chromosomes fail to separate properly, therefore leading to a gamete that has an extra X chromosome when it fertilizes. The clinical presentation can vary, but the presence of the extra X chromosome is the key factor in the expression of Klinefelter's Syndrome.