IGHG1 and plasma cell myeloma: Analyzing the expression changes of markers in the four myeloma cell subpopulations with the predicted developmental trajectories (Figure 4M), IGLC3 was the most highly expressed in the initiation segment and gradually decreased with the proposed chronological trajectory, IGHA1 was relatively evenly expressed throughout the developmental trajectory, and IGHG1 and IGHG4 were elevated with the proposed chronological trajectory, and were more highly expressed in the terminal segment.