 This happens early in embryonic development at random in mammals, except in marsupials and in some extra-embryonic tissues of some placental mammals, in which the X chromosome from the sperm is always deactivated.In humans with more than one X chromosome, the number of Barr bodies visible at interphase is always one fewer than the total number of X chromosomes.For example, people with Klinefelter syndrome (47,XXY karyotype) have a single Barr body, and people with a 47, XXX karyotype have two Barr bodies.