Sydney Brenner’s 2002 Nobel prize lecture envisaged humans as the model organism of choice in an age of genomics. This seminar will outline our work on extreme growth disorders, a group of human single gene disorders which we have exploited to gain insights into fundamental cellular processes. I will speak about an enigmatic protein involved in DNA replication and how AI has shed light on its molecular function. I will also talk about our ongoing work on a gain of function DNMT3A mutation, where we have been using haematopoiesis to investigate how it impacts globally on cell number and organism size.