Skewing of X chromosome inactivation. Products from PCR with Hpa II digested and mock-digested templates. Order of lanes: 100-bp ladder; then, paired, PCRs of digested and mock-digested DNA from: fibroblasts from one twin, whole blood from that twin, fibroblasts from second twin, whole blood from second twin, and fibroblasts from mother; then, as controls, Hpa II-digested and mock-digested male DNA as digestion controls, Hpa II-“digested” TE and Hpa II-digested female DNA as nonskewed control.