Joe Hin Tjio

Tjio (whose name is pronounced CHEE-oh) 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. Tjio was educated in Dutch colonial schools, trained in agronomy in college, and did research on potato breeding. He was imprisoned for 3 years and tortured by the Japanese in a concentration camp during World War II.

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 and vacations in Sweden working with Professor Albert Levan in Lund.

It was during one of his vacation stays in Lund that Tjio made his discovery of the correct human chromosome count. For fully a half century it had been accepted that humans normally have 48 chromosomes. Now Tjio knew "the chromosome number of man" was 46. Tjio's revolutionary finding was published (with Levan as his co-author) in the Scandinavian journal Hereditas on January 26, 1956, only a month and four days after the discovery.

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 balance of his long 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.

• Tjio JH, Levan A. The chromosome number of man. Hereditas vol. 42: pages 1–6, 1956.