Professor Choo is distinguished for his contributions to human molecular genetics. He was the first to clone the gene for human blood-clotting factor IX, leading to new therapies for haemophilia B. His pioneering work on the human centromere has revolutionised our understanding of chromosome stability and replication. He was the first to describe the epigenetic formation of neurocentromeres in chromosomal fragments, at that time a novel concept that broke the paradigms of eukaryotic chromosome structure and function. His work on the centromere has lead to greater understanding of chromosome non-disjunction, and given impetus to the use of synthetic human mini-chromosomes as vectors for gene therapy.