In a person carrying several X chromosomes, how many remain active in each cell?

1. X inactivation exists to compensate for a double genetic dose of X chromosome genes. 2. An individual carrying an abnormal number of X chromosomes inactivates all but one in each cell. 3. In every type of Klinefelter syndrome, every X chromosome except one undergoes inactivation. 4. Each inactivated X condenses into a Barr body, so several Barr bodies can be seen in one nucleus. 5. Only one X therefore stays active, whatever the total number present. 6. This compensation is why sex chromosome abnormalities have milder effects than autosomal ones. 7. Inactivated X chromosomes still express a few genes, so compensation is not perfect. _Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 13 "Modern Understandings of Inheritance", section 13.2 Chromosomal Basis of Inherited Disorders_