studies of somatic tissues and cultured cells , including fibroblast clones , from human embryos heterozygous for the electrophoretic variants of glucose-6-phosphate dehydrogenase confirm that one x chromosome is inactivated very early in embryonic development and indicate that x inactivation has occurred in the majority of cells from a variety of tissues at least by 5 weeks from conception .
C0043292
x chromosome
C0043297
x inactivation