Joe Hin Tjio (; 2 November 1919 – 27 November 2001), was an Indonesian-born American cytogeneticist. He was renowned as the first person to recognize the normal number of human

chromosome A chromosome is a package of DNA containing part or all of the genetic material of an organism. In most chromosomes, the very long thin DNA fibers are coated with nucleosome-forming packaging proteins; in eukaryotic cells, the most import ...

s on 22 December 1955 at the Institute of Genetics of the University of Lund in Sweden, where he was a visiting scientist.

Early life

Tjio was born to Indonesian parents of Chinese origin in

Pekalongan Pekalongan () is a city of Central Java, Indonesia. It was formerly the seat of Pekalongan Regency on the northern coast of the province, but is now an independent municipality within the province. It covers a land area of 45.25 km2 and had a p ...

Java Java is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea (a part of Pacific Ocean) to the north. With a population of 156.9 million people (including Madura) in mid 2024, proje ...

, then part of the

Dutch East Indies The Dutch East Indies, also known as the Netherlands East Indies (; ), was a Dutch Empire, Dutch colony with territory mostly comprising the modern state of Indonesia, which Proclamation of Indonesian Independence, declared independence on 17 Au ...

and later known as Indonesia. His father was a photographer. Tjio was educated in Dutch colonial schools, trained in

agronomy Agronomy is the science and technology of producing and using plants by agriculture for food, fuel, fiber, chemicals, recreation, or land conservation. Agronomy has come to include research of plant genetics, plant physiology, meteorology, and ...

in college, and did research on potato breeding. He was imprisoned for 3 years and tortured by the Japanese in a

concentration camp A concentration camp is a prison or other facility used for the internment of political prisoners or politically targeted demographics, such as members of national or ethnic minority groups, on the grounds of national security, or for exploitati ...

during

World War II World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...

Career

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 Zaragoza (), traditionally known in English as Saragossa ( ), is the capital city of the province of Zaragoza and of the autonomous communities of Spain, autonomous community of Aragon, Spain. It lies by the Ebro river and its tributaries, the ...

in Spain and spent his summers in Sweden working with Professor Albert Levan in Lund. In 1953, a lab mistake involving mixing

HeLa cells HeLa () is an immortalized cell line used in scientific research. It is the oldest human cell line and one of the most commonly used. HeLa cells are durable and prolific, allowing for extensive applications in scientific study. The line is ...

with the wrong liquid led Tjio and Levan to develop better techniques for staining and counting chromosomes. It allowed researchers for the first time to see and count each chromosome clearly in the HeLa cells with which they were working. They were the first to show that humans have 23 pairs of chromosomes rather than 24, as was previously believed. This was important for the study of developmental disorders, such as Down syndrome, that involve the number of chromosomes. Tjio made his discovery of the correct human chromosome count (46 chromosomes, rather than 48 as counted in 1921 by Theophilus Painter) in 1955 and the findings were published (with Levan as his co-author) in the Scandinavian journal '' Hereditas'' on 26 January 1956. In 1958 Tjio went to the United States and in 1959 he joined the staff of the

National Institutes of Health The National Institutes of Health (NIH) is the primary agency of the United States government responsible for biomedical and public health research. It was founded in 1887 and is part of the United States Department of Health and Human Service ...

Bethesda, Maryland Bethesda () is an unincorporated, census-designated place in southern Montgomery County, Maryland, United States. Located just northwest of Washington, D.C., it is a major business and government center of the Washington metropolitan region ...

. He received his Ph.D. in biophysics and cytogenetics from the

University of Colorado The University of Colorado (CU) is a system of public universities in Colorado. It consists of four institutions: the University of Colorado Boulder, the University of Colorado Colorado Springs, the University of Colorado Denver, and the U ...

. He spent the balance 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 Gaithersburg ( ) is a city in Montgomery County, Maryland, United States. At the time of the 2020 United States census, Gaithersburg had a population of 69,657, making it the third-largest incorporated city and the ninth-most populous communit ...

where he died in 2001 aged 82.

Works

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

References

External links

Human chromosome count
in MedTerms Medical Dictionary {{DEFAULTSORT:Tjio, Joe Hin 1919 births 2001 deaths American geneticists American people of Chinese-Indonesian descent Indonesian emigrants to the United States Indonesian people of Chinese descent People from Pekalongan American people of Chinese descent Hakka scientists