Different XCI patterns in heterozygous hESC lines. (A) shows random XCI in hES-25, hES-26 and hES-35 where two active and two inactive alleles of the HUMARA gene are detected. The peak area ratios between the two active or inactive alleles are 50:50, 64:36 and 60:40 respectively. (B) shows skewed XCI of hES-20, hES-27 and hES-39 where only one active allele and another different inactive allele of the HUMARA gene are detected. (C) shows normal female blood DNA as a control for random XCI (two active and two inactive alleles, 183 and 200 bp, respectively), and (D) shows normal male blood DNA with only a 190 bp active allele and no inactive allele detected. X-axis indicates the size (bp) of DNA product.