Dr James (Jim) Peacock has made significant contributions to the understanding pf the molecular architecture of chromosomes—the establishment of iso-chromatic labelling indicating subunit structures; reunion following breakage is limited by the 3' - 5' reunion following polynucleotide polarities of the subunits, which polarities are opposed, but not uniform along the chromosome. He has demonstrated the separation in time of DNA replication and crossing over by breakage-reunion, extending the classical work of Creighton and McClintock. Peacock has established the basis of meiotic drive (segregation distortion) in terms of sperm morphogenesis in Drosophila and has shown that highly repeated DNA sequences occur in the centromeric regions of chromosomes, are chromosome-specific, and highly conserved. These sequences have a functional role, perhaps in relation to homologous chromosome recognition.