Theodore T. Puck, 89, a prominent genetics researcher who devised techniques for growing human cells in the laboratory and who helped determine the number of chromosomes in a gene, died Nov. 6 in a Denver hospital of complications from a fall.

In a career spanning more than 60 years, Dr. Puck was credited with many advances that have become basic elements of research in oncology and the human genome and have helped unravel some of the mysteries of genetic diseases. He performed some of the first studies on radiation doses and the effects of environmental contaminants on DNA.

He was primarily known for his landmark studies in the 1950s in which he created the proper conditions in which human cells could grow and propagate in a petri dish. His incubating technique, called somatic cell genetics, is widely used and has been a considerable boon to biomedical research.

Dr. Puck, who in 1961 founded the Eleanor Roosevelt Institute of Cancer Research (now part of the University of Denver), was among the first scientists to examine the effects of radiation on the human body. He concluded that a lethal radiation dose was only 1 percent of what scientists had previously believed and that even low levels of exposure could cause mutations. His studies have helped doctors develop safe dosages of radiation in the treatment of cancer.

In the 1950s, Dr. Puck noticed an obscure study by a Chinese researcher on the makeup of chromosomes, or the basic human genetic map. He invited the young scholar, J.H. Tijo, to study with him at the University of Colorado, and together they examined microscopic photographs of thousands of cells.

At a time when most scientists believed the human genetic code contained 47 or 48 chromosomes, Dr. Puck and Tijo proved that it consisted of 46 chromosomes arranged in 23 pairs. In 1959, Dr. Puck convened a conference at which scientists devised a method for numbering the chromosomal pattern, which continues to be known as the Denver system. As a result, the genetic links of Alzheimer's disease, Down syndrome and other disorders can be more fully understood.

"I think he should have won the Nobel Prize," said David Patterson, president of the Eleanor Roosevelt Institute and a scientific colleague of Dr. Puck's since 1971. "I don't know why he didn't. He was sort of a shy person who didn't promote himself outside the scientific community. He would rather work in the lab."

Theodore Thomas Puckowitz -- he later shortened his name -- was born in Chicago and graduated from the University of Chicago with bachelor's and doctoral degrees in physical chemistry in 1937 and 1940, respectively.

During World War II, he served on an Army commission studying airborne infections. He joined the University of Colorado's medical center in Denver in 1948 and remained affiliated with the university for the rest of his life.

In 1958, he received the prestigious Albert Lasker Award for his work on human cells, followed by many other honors. He was a fellow of the Los Alamos National Laboratories, an editorial board member of the Encyclopaedia Britannica and a member of the National Academy of Science and the American Academy of Arts and Sciences.

Dr. Puck was a renowned teacher as well as a researcher, and one of his students, Sidney Altman, received the Nobel Prize in chemistry in 1989.

"He trained some of the best human geneticists in the world," said Patterson, Dr. Puck's longtime colleague. "He was inspiring and was very enthusiastic about how what he was doing would have significance for human health."

Dr. Puck continued to work in his laboratory at the Eleanor Roosevelt Institute until the week before his death.

Survivors include his wife of 59 years, Mary Hill Puck of Denver; three daughters, Dr. Laurel Northup and Dr. Jennifer Puck, both of Bethesda, and Dr. Stirling Puck of Santa Fe, N.M.; and seven grandchildren.

Theodore Puck studied DNA.