Description
Dosage compensation restores a balanced network of gene expression between autosomes and sex chromosomes in males (XY) and females (XX). In mammals, this is achieved by doubling the expression of X-linked genes in both sexes, together with X inactivation in females. X up-regulation may be controlled by DNA sequence based and/or epigenetic mechanisms that double the X output potentially in response to an autosomal counting factor. Human triploids with either one or two active X chromosomes (Xa) provide a mean to test X chromosome expression in the presence of three sets of autosomes, which will help understand the underlying mechanisms of X up-regulation.