Alfred H. Sturtevant

• Born: November 21, 1891
• Birthplace: Jacksonville, Illinois
• Died: April 5, 1970
• Place of death: Pasadena, California

Background and Education

American geneticist Alfred Sturtevant is best known for developing a method for mapping the location of genes on a chromosome. He began studying the genetics of the fruit fly in 1910 as one of Thomas Hunt Morgan's students in the famous "fly room" laboratory at Columbia University. Later, he was a professor at the California Institute of Technology. He was awarded the National Medal of Science in 1968.

Alfred Henry Sturtevant was born on November 21, 1891, in Jacksonville, Illinois. He was the last of six children born to Harriet Evelyn Morse and her husband Alfred Henry Sturtevant. The elder Sturtevant taught mathematics at Illinois College, but later left the academic life to become a farmer. When Alfred was seven years old, his family relocated to southern Alabama.

In Alabama, Alfred attended school in a one-room schoolhouse. He stayed there until his high school years, when he transferred to a larger public school in the town of Mobile. He showed an early interest in genetics, especially in pedigrees. As a boy, he amused himself by making pedigrees of his family's farm horses. He later published a more sophisticated version of that same project, demonstrating the mode of inheritance of coat color in horses.

Sturtevant enrolled at Columbia University in 1908, when he was seventeen. His older brother Edward taught there at Barnard College; he later became a professor of linguistics at Yale, and a noted expert in the Hittite language. Alfred would not have been able to complete his education without the assistance of his brother, who took him into his home and was a great source of encouragement. In fact, it was Edward who suggested that Alfred contact Columbia professor Thomas Hunt Morgan to share his studies on inheritance of coat color in horses. Morgan was impressed enough to suggest publishing the paper, and also recruited Alfred to join his dynamic research group in the "fly room."

Morgan's research group was unique because of the casual way in which discussions were conducted. Many academic institutions in the early twentieth century were quite formal, both in dress (even students wore suits and ties) and conduct. At that time, ideas and instructions usually came from professors. Unsolicited input from junior team members was generally not considered appropriate. In Morgan's lab, however, debate and the free exchange of ideas were encouraged. This stimulated a creative atmosphere that suited Sturtevant's quick mind perfectly. Sturtevant was soon recognized as the leader of the students, and one of Morgan's closest confidants.

Mapping the Chromosome

Sturtevant is perhaps best remembered for a project he completed as an undergraduate. After a discussion with Professor Morgan, it occurred to Sturtevant that he could figure out in which order genes were arranged on chromosomes. As the story goes, he skipped his homework and stayed up most of the night working on the gene map.

Chromosomes are responsible for passing heritable traits from generation to generation. Children inherit copies of their parents' chromosomes, creating family resemblances. However, a process called crossover changes the chromosomes slightly before they are passed on. Those changes make each child unique, different from both the parents and siblings. Sturtevant would use the mechanism of crossing over to make his gene map.

On the sub-microscopic level, chromosomes are made up of DNA that is wound around proteins like thread on small spools. Certain stretches of DNA along those chromosomes are called genes. Genes code for the body's proteins. The result is a heritable code not only for the basic body plan, but also for traits like coloration of eyes and skin. In humans, even the tendency for certain personality traits, such as being introverted or extroverted, can be inherited.

Each human cell contains 46 chromosomes, with 23 inherited from the mother and 23 inherited from the father. When gametes (sperm and ova) are being produced, the chromosomes in those cells undergo crossover. Each chromosome pairs up with the corresponding one from the other parent. The chromosome pairs (except for sex chromosomes) carry corresponding information. For example, both chromosomes of a homologous pair might carry information for eye color. Depending on the color of the parents' eyes, that information may match or be different.

During crossover, a section breaks off the end of a maternal chromosome and is traded for a corresponding piece broken off the paternal chromosome. The process creates immense genetic diversity. New chromosomes are created, with genes in new combinations never before found in either parent.

Morgan's team was already aware of crossover. In their experiments with fruit flies, the expected proportions of certain traits in offspring were altered if crossing over occurred. They knew that some genes had to be carried on the same chromosome, because they were almost always inherited together. For example, most red-haired people also have freckles, because red hair and freckles are carried near each other on the same chromosome. They are "linked," but they can be separated by crossing over.

Sturtevant realized that the frequency with which traits are separated by crossover could be used as a measure of how far apart they are on the chromosome. The closer together they are, the less likely they are to be separated. Genes on opposite ends of the same chromosome will almost certainly be separated by crossing over. By mating certain strains of fruit flies together and counting the kinds of offspring produced, Sturtevant was able to discern the order of genes on a chromosome.

Genetics Research

Sturtevant finished his Ph.D. in 1914, but remained at Columbia to continue his genetics research. He married Phoebe Curtis Reed in 1922, and six years later they moved out to Pasadena, California. Sturtevant took a job teaching genetics at the California Institute of Technology, where he would spend the rest of his career.

Sturtevant had a brilliant mind, and loved to accumulate information on almost every topic. For relaxation, he enjoyed doing complex puzzles and reading the encyclopedia. In conversation, he was sometimes hard to understand, since he treated everyone as though they were as intelligent and well read as he was. This trait was also apparent in the undergraduate genetics textbook he co-wrote with the 1958 Nobel Prize winner George Wells Beadle. The book was never widely adopted, mainly because it was beyond the level of understanding of most students.

Sturtevant's genetics research involved a variety of plants and animals. His discoveries included a gene that causes intersexuality (being between male and female) in fruit flies. That work made researchers realize that the inheritance of gender is more complex than previously believed. He also found the first reparable mutation in a gene, thus opening the door to future treatments for genetic diseases. The field of embryology was energized by his discovery of fate-mapping, which allows scientists to determine which cells in a well-developed embryo were derived from which cells from an earlier stage of development.

In 1932, the Carnegie Endowment for International Peace provided support that allowed Sturtevant to spend a year in England and Germany as a visiting professor. After returning to California, he spent much of the next decade focusing on the genetics of fruit flies. In collaboration with George Wells Beadle, he looked at the effect of inversions (DNA sequences inserted backwards into the genome) on chromosomal crossover.

Sturtevant was one of the first scientists to go public with concerns about public safety in the American West, where nuclear bombs were being tested. He was president of the American Association for the Advancement of Science in 1954, and in his address to that organization he shared his concerns with the scientific community. He feared that radioactive fallout could cause genetic damage in communities downwind from nuclear test sites. Sturtevant's son later clarified his father's position, saying that he was not opposed to the testing itself, but felt it was fair that the public be warned of the danger.

In February 1968, President Lyndon B. Johnson awarded Sturtevant the National Medal of Science in a ceremony at the White House. This prestigious award was in recognition of his many discoveries in the field of Drosophila (fruit fly) genetics. Sturtevant passed away on April 5, 1970.

Bibliography

"Dr. Alfred Sturtevant, 78, Dies; Geneticist Won U.S. Medal." The New York Times, 7 Apr. 1970, www.nytimes.com/1970/04/07/archives/dr-alfred-sturtevant-78-dies-geneticist-won-us-medal.html. Accessed 30 Oct. 2020.

Gleason, Kevin. "Alfred Henry Sturtevant (1891–1970)." The Embryo Project Encyclopedia, The Embryo Project at Arizona State University, Arizona Board of Regents, 20 May 2017, embryo.asu.edu/pages/alfred-henry-sturtevant-1891-1970. Accessed 30 Oct. 2020.

Smith, Douglas. "The First Genetic-Linkage Map." Caltech, California Institute of Technology, 21 Mar. 2013, embryo.asu.edu/pages/alfred-henry-sturtevant-1891-1970. Accessed 30 Oct. 2020.