David L. Nelson is currently Professor in the Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas. His background lies in human genetics and the human genome project, with emphasis on the human X chromosome. He has participated in the identification of the gene mutated in fragile X syndrome, the first disease caused by trinucleotide repeat expansion. His laboratory continues to investigate this and other X-linked human genetic disorders, and to develop approaches to the study of common, complex disorders with genetic influences. Relevant to the LOH, Dr. Nelson has developed an interest in defining genetic differences amongst man and the higher primates. His group is pursuing identification of regions of the human genome at the sites of chromosome-scale rearrangements that have occurred in recent evolutionary history. Dr. Nelson's doctoral work was carried out at Massachusetts Insitute of Technolgy under the supervision of Dr. David Housman. He trained at the NIH and at Baylor as a postdoctoral fellow with Drs. Robert Lazzarini and C. Thomas Caskey, respectively. He has been a member of the faculty at Baylor since 1989.