The extra X chromosome observed in Klinefelter syndrome originates from the mother in approximately 60% of cases and from the father in 40%. This condition is not a genetic inheritance where parents are carriers, nor can it be detected by routine parental blood tests. It typically results from chromosomal division errors that occur during the formation of egg or sperm cells. In cases where the extra X chromosome originates from the mother, advanced maternal age (>35) is a significant risk factor. For instance, while the risk of 47,XXY in a child of a 33-year-old mother is approximately 1/2500, this risk increases to 1/300 for a child of a 43-year-old mother. Recent studies also indicate that older fathers have an increased likelihood of having an extra X chromosome in their sperm, which can also influence the risk of the syndrome.