As Tonegawa explored further, he discovered a pattern that described the differences between immature B cells and mature ones. Each of them shared key genetic material with one major variance: In the immature B cell, that crucial genetic material was mixed in with, and separated by, a whole array of other genetic material. As the B cell matured into a fully functioning immune system cell, much of the genetic material dropped out. And not just that: In each maturing B cell, different material dropped out.
