Variability of postnatal ossification timing and evidence for a “dosage” effect

Abstract

Although absolute variability in postnatal ossification timing is generally larger in boys than in girls, relative, conception-corrected variability is significantly larger in girls, suggestive of a “dosage” effect and consistent with the hypothesis of partial X-linkage. These findings, together with the excess of sister-sister over brother-brother timing similarities are inconsistent with the hypothesis of selective inactivation of either the paternal or the maternal X chromosome.