Joe Hin Tjio

Joe Hin Tjio was an Indonesian-born American cytogeneticist who was renowned as the first person to recognize the normal number of human chromosomes on December 22, 1955 at the Institute of Genetics of the University of Lund in Sweden, where Tjio was a visiting scientist. He was a brilliant experimentalist who developed delicate new techniques for separating chromosomes from the nucleus of the cell. His discovery, which rewrote the textbooks, showed that the majority of cells in the body normally contain 46 chromosomes, arranged in 23 pairs, rather than 48 as previously thought. This breakthrough helped transform cytogenetics into a field of major medical importance, as it established the link between abnormal chromosomes and certain diseases, such as Down's syndrome. ² Tjio was born to Indonesian parents of Chinese origin in Pekalongan, Java, then part of the Dutch East Indies and later known as Indonesia. His father was a photographer and taught him how to develop photographs and make prints in the darkroom, which proved a valuable asset for his son when he came to photographing microscope images. He was educated in Dutch colonial schools and trained in agronomy in college. He did research on potato breeding and was imprisoned for three years and tortured by the Japanese in a concentration camp during World War II. ² After the war ended, Tjio went to the Netherlands, whose government provided him with a fellowship for study in Europe. He worked in plant breeding in Denmark, Spain and Sweden. From 1948 to 1959 he did plant chromosome research in Zaragoza in Spain and spent his summers in Sweden working with Professor Albert Levan in Lund. ² In 1955, Tjio made his discovery of the correct human chromosome count and the findings were published (with Levan as his co-author) in the Scandinavian journal Hereditas on January 26, 1956. In 1958 Tjio went to the United States and in 1959 he joined the staff of the National Institutes of Health in Bethesda, Maryland. He received his Ph.D. in biophysics and cytogenetics from the University of Colorado. He spent the rest of his career at the NIH in human chromosome research. He was named scientist emeritus in 1992, but maintained a laboratory for the next five years. In 1997, he retired to Gaithersburg, Maryland. ² He died of a heart attack in Gaithersburg on 27 November 2001 at the age of 82. ²