the expected level of X-linked gene expression in males would be 50% that of females, thus the plant practices some degree of dosage compensation but, because male expression is not 100% that of females, it has been suggested that S. latiforia and its dosage compensation system is still evolving. Additionally, in plant species that lack dimorphic sex chromosomes, dosage compensation can occur when aberrant meiotic events or mutations result in either aneuploidy or polyploidy. Genes on the affected chromosome may be upregulated or down-regulated to compensate for the change in the normal number of chromosomes present. Reptiles Research into dosage compensation has been carried out in six species of toxicoferan reptiles and in one species of softshell turtle. Two species of caenophidian snake (one which belongs to the family Viperidae and the other to the family Colubridae) have been investigated and both of these exhibit female heterogametic sex determination systems (ZZ\ZW) and have incomplete compensation without balance. The Komodo dragon exhibits incomplete compensation without dosage balance in their independently evolved ZZ/ZW system. In the XX/XY system of Basiliscus vittatus and multiple neo-sex chromosomes with male heterogamety in the pygopodid gecko Lialis burtonis incomplete compensation without dosage balance were also seen. The Green anole (Anolis carolinensis; Dactyloidea), has XX/XY sex determination and unlike the other squamates studied to date has complete dosage compensation with dosage balance. In the Florida softshell turtle (Apalone ferox) with ZZ/ZW sex chromosomes, the lack of dosage balance in the expression of Z-linked genes was also found. X chromosome inactivation and embryonic stem cells XCI is initiated very early during female embryonic development or upon differentiation of female embryonic stem (ES) cells and results in inactivation of one X chromosome in every female somatic cell. This process is initiated very early during development, around the two- to eight-cell stage and is maintained in the developing extra-embryonic tissues of the embryo, including the fetal placenta. Xist RNA induces heterochromatinization of the X chromosome by attracting chromatin modifiers, involved in gene silencing. Xist RNA is tightly associated with the Xi and it is required for X Chromosome Inactivation to occur in cis. Knockout studies in female ES cells and mice have shown that X chromosomes bearing a deletion of the Xist gene are unable to inactivate the mutated X. Most of the human female ES cell lines display an inactivated X chromosome already in the undifferentiated state characterized by