Final answer:
People with Klinefelter syndrome have an XXY chromosome constitution, and the extra X undergoes inactivation, observable as Barr bodies. This condition presents in males with certain physical and developmental characteristics. It is caused by nondisjunction during meiosis.
Step-by-step explanation:
People with Klinefelter syndrome have an XXY chromosome constitution. This condition corresponds to phenotypically male individuals who may exhibit features such as small testes, enlarged breasts, reduced body hair, and potential learning difficulties. The extra X chromosome in Klinefelter syndrome undergoes inactivation to compensate for the excess genetic dosage, which is visible as several Barr bodies in each cell nucleus. Contrary to Klinefelter syndrome, Turner syndrome is characterized by an XO genotype, representing a single sex chromosome, and is observed in phenotypically female individuals.
In the case of an error in meiosis leading to the XXY genotype of Klinefelter syndrome, a nondisjunction event occurs where the sex chromosomes fail to separate properly, resulting in an individual with an additional X chromosome.