Alfred Henry Sturtevant was an American influential geneticist and zoologist, best known for his demonstrations of the principles of gene mapping. This discovery had a profound effect on the field of genetics and led to projects, that mapped both animal and human chromosomes. Also, he was an author of several important scientific works.
Background
Alfred Sturtevant was born on November 21, 1891, in Jacksonville, Illinois, United States. He was a son of Alfred Henry Sturtevant, a teacher of Mathematics, and Harriet (Morse) Sturtevant. Alfred had five siblings, one of which was Edgar Howard Sturtevant, a linguist. Also, Alfred was a grandchild of Julian Monson Sturtevant, a founding professor and second president of Illinois College.
When Sturtevant was seven years old, his father, Alfred Henry Sturtevant, left his teaching job and moved the family to Alabama to pursue farming.
Education
In his early years, Alfred attended a high school in Mobile, Alabama, which was fourteen miles from his home and accessible only by train. In 1908, he enrolled in Columbia University in New York City, boarding with his older brother, Edgar, who taught linguistics at Columbia’s Barnard College. Edgar and his wife played a significant role in young Sturtevant's life. They sent him Columbia’s entrance examination, pulled strings to get him a scholarship and welcomed him into their home in Edgewater, New Jersey, for four years. Edgar was also responsible for steering his brother toward a career in the sciences.
It was Edgar, who encouraged Alfred to write a paper on the subject of color heredity in horses and to submit the draft to Columbia University’s Thomas Hunt Morgan, the future Nobel Laureate geneticist. The paper used the recently rediscovered theories of Gregor Mendel, the nineteenth-century Austrian monk and founder of genetics, to explain certain coat-color inheritance patterns in horses. Sturtevant somehow mastered this subject in spite of his color-blindness.
As a result of his paper on horses, which was published in 1910, Sturtevant was given a desk in Morgan’s famous "fly room", a small laboratory, dedicated to genetic research, using Drosophila (fruit flies) as subjects.
Studying under Thomas Hunt Morgan, who believed, that the relative distance between genes could be measured if the crossing-over frequencies could be determined, Alfred developed a practical method for determining this frequency rate. He began by studying six sex-linked traits and measured the occurrence of this related trait. The more frequently the traits occurred, Sturtevant reasoned, the closer the genes must be. He then calculated the percentages of crossing-over between the various traits. From these percentages, he determined the relative distance between the genes on the chromosome, the first instance of gene mapping. This major discovery, which Sturtevant published in 1913 at the age of twenty-two, eventually enabled scientists to map human and animal genes.
In 1914, Sturtevant received his Doctor of Philosophy degree from Columbia University.
In 1914, after graduation from Columbia University, Alfred began working as an investigator in Thomas Hunt Morgan's lab at the Carnegie Institution for Science in Washington, D.C., a post he held till 1928. Along with C. B. Bridges, Hermann Joseph Muller and Morgan, he formed part of an influential research team, that made significant contributions to the fields of genetics and entomology. Alfred later described the lab as highly democratic and occasionally argumentative, with ideas being heatedly debated. The 16x24-foot lab had no desks, no separate offices, one general telephone and very few graduate assistants. However, Sturtevant thrived in this environment. He worked seven days a week, reserving his mornings for Drosophila research and his afternoons for reading the scientific literature and consulting with colleagues. Together with his co-workers, Alfred raised research standards and elevated research writing to an art form. Together, they also perfected the practice of chromosome mapping, using Sturtevant’s methods to develop a chromosome map of Drosophila, detailing the relative positions of fifty genes.
It was in 1914, that Sturtevant published a paper, that documented cases of double crossing-over, in which chromosomes, that had already crossed-over, broke with one another and recrossed again. His next major paper, published in 1915, concerned the sexual behavior of fruit flies and concentrated on six specific mutant genes, that altered eye or body color, two factors, that played important roles in sexual selection. He then showed, that specific genes were responsible for selective intersexuality.
In later years, he discovered a gene, that caused an almost complete sex change in fruit flies, miraculously transforming females into near males. In subsequent years, researchers identified other sex genes in many animals, as well as in humans. These discoveries led to the development of the uniquely twentieth-century view of sex as a gene-controlled trait, which is subject to variability.
During the 1920's, Sturtevant and Morgan examined the unstable bar-eye trait in Drosophila. Most geneticists at that time believed, that bar-eye did not follow the rules of Mendelian heredity. In 1925, Sturtevant showed, that bar eye involved a recombination of genes, rather than a mutation, and that the position of the gene on the chromosome had an effect on its action. This discovery, known as the position effect, contributed greatly to the understanding of the action of the gene.
In 1928, Morgan received an offer from the California Institute of Technology to develop a new Division of Biological Sciences. Sturtevant followed his mentor to California, where he became the first professor of genetics and researcher at Caltech’s Kerckhoff Laboratory, the positions he held till 1947. Sturtevant continued working with fruit flies and conducted genetic investigations of other animals and plants, including snails, rabbits, moths, rats and the evening primrose, Oenothera.
In 1929, Sturtevant discovered a "sex ratio" gene, that caused male flies to produce X sperm almost exclusively, instead of X and Y sperm. As a result, these flies’ offspring were almost always females. In the early 1930's, giant chromosomes were discovered in the salivary glands of fruit flies. Under magnification, these chromosomes revealed cross patterns, which were correlated to specific genes. The so-called "physical" map, derived from these giant chromosomes, did not exactly match Sturtevant’s "relative" location maps. In the physical map, some of the genes tended to cluster toward one end of the chromosome and the distances between genes was not uniform. But the linear order of the genes on the chromosome matched Sturtevant’s relative maps gene for gene. This discovery confirmed, that Sturtevant had been correct in his assumptions about chromosomal linearity.
In 1932, Sturtevant took a sabbatical leave and spent the year in England and Germany as a visiting professor of the Carnegie Endowment for International Peace. When he returned to the United States, he collaborated with his Caltech colleague Theodosius Dobzhansky, a Russian-born geneticist, on a study of inversions in the third chromosome of Drosophila pseudoohscura. In the 1940's, Sturtevant studied all of the known gene mutations in Drosophila and their various effects on the development of the species.
From 1947 to 1962, Alfred served as a Thomas Hunt Morgan Professor of Biology at Caltech’s Kerckhoff Laboratory, California Institute of Technology. His most significant scientific contribution during that time occurred in 1951, when he unveiled his chromosome map of the indescribably small fourth chromosome of the fruit fly, a genetic problem, that had puzzled scientists for decades.
During the 1950's and 1960's, Sturtevant turned his attention to the iris and authored numerous papers on the subject of evolution. He became concerned with the potential dangers of genetics research and wrote several papers on the social significance of human genetics. In a 1954 speech to the Pacific Division of the American Association for the Advancement of Science, he described the possible genetic consequences of nuclear war and argued, that the public should be made aware of these possible cataclysmic hazards before any further bomb testing was performed. One of his last published journal articles, written in 1956, described a mutation in fruit flies, that, by itself, was harmless, but which proved lethal in combination with another specific mutant gene.
In 1962, Sturtevant was made a Professor Emeritus by Caltech’s Kerckhoff Laboratory, California Institute of Technology. He spent the better part of the early 1960's, writing his major work, "A History of Genetics", which was published in 1965.
Alfred Henry Sturtevant was a prominent geneticist, who gained prominence for the development of a technique for mapping the location of specific genes of the chromosomes in the fruit fly Drosophila. Sturtevant's work on the Drosophila genome enabled geneticists to further map chromosomes of higher organisms, including human beings.
Sturtevant proved, that the mechanism of crossing-over (the exchange of genes between chromosomes) could be prevented in Drosophila. Alfred also discovered, that a position of the gene on the chromosome had an effect on its action. This phenomenon became later known as the position effect.
Moreover, Alfred determined, that genes were arranged on chromosomes in a linear fashion, like beads on a necklace. He showed, that the gene for any specific trait was in a fixed location (locus). His work also helped to determine genetic role in sexual selection and development, and displayed the importance of chromosomal crossing-over in mutations.
During his lifetime, he received several awards, including John J. Carty Award for the Advancement of Science in 1965, National Medal of Science in 1967 and others.
Quotations:
"There is a reference in Aristotle to a gnat, produced by larvae, engendered in the slime of vinegar. This must have been Drosophila."
Membership
Alfred was a member of the United States National Academy of Sciences and American Philosophical Society among others.
president of Pacific Division
American Association for the Advancement of Science
,
United States
1953 - 1954
president
American Society of Zoologists
,
United States
1934
president
Genetics Society of America
,
United States
1944
Personality
Alfred possessed a near photographic memory and wide-ranging interests. His only shortcoming as a researcher was his incessant pipe-smoking, which often left flakes of tobacco ash mixed in with the samples of fruit flies.
Connections
Alfred married Phoebe Curtis Reed in 1923 and the couple honeymooned in Europe, touring England, Norway, Sweden and Holland. Their marriage produced three children, the most notable of which was William Curtis Sturtevant, an anthropologist and ethnologist.
Father:
Alfred Henry Sturtevant
Alfred Henry Sturtevant was a teacher of Mathematics.
Mother:
Harriet (Morse) Sturtevant
child:
William Curtis Sturtevant
Grandfather:
Julian Monson Sturtevant
Julian Monson Sturtevant was an American author and educator.
