born February 17, 1889, Sundance, Wyoming, USA

Except for some early taxonomic studies, Metz’s investigations centered largely on chromosomes. These investigations began when he was a graduate student at Columbia University under E.B. Wilson and in association with T.H. Morgan’s Drosophila group. At that time 1912-1914, the chromosome theory of heredity, with its basic concepts of “individuality and continuity” of chromosomes, was in dispute. Through cytological study of different species of Drosophila, Metz in 1914 helped to establish the validity of these concepts and to throw light on the evolution of chromosomes. Strong evidence was provided that individually identifiable chromosomes were qualitatively different from others and maintained their characteristics from generation to generation. It was also found that long V-shaped chromosomes in some species were each represented in other species by two short rod-shaped chromosomes, each comparable to one arm of a V. Based on this principle, the different types of groups could readily be arranged in series suggesting evolutionary sequence.

If these interpretations were correct, it followed that similar genes should be present in homologous chromosomes, or chromosome arms, of different species, and that these might be detected genetically by securing and comparing mutant characters. Progress in such comparative genetic studies was made possible largely because the work of Morgan and his associates on D. melanogaster provided evidence about mutants and their linkage relations in this species which could be used for comparison. The cooperation of A.H. Sturtevant in securing specimens and in discussions also helped materially. Significant results were secured by 1915-1916 and, with the aid of assistants, the work was extended to include cytological study of 26 species and genetic study of 3 species in addition to D. melanogaster. The results gave strong support to the initial interpretations. Genes for similar mutants appeared to be not only in corresponding chromosomes but in some cases arranged in similar sequence. Evidence of less conspicuous changes was also found. While these studies were under way, D.E. Lancefield in 1922 secured similar genetic results in studies on another species of Drosophila, and Sturtevant in 1920, by securing hybrids between D. melanogaster and a very similar species, D. simulans, demonstrated the presence of homologous genes in homologous chromosomes of these species.

At this stage, about 1923, the main purposes of Metz’s studies had been accomplished. The field of cytogenetics had advanced greatly, with the fundamental importance of chromosomes recognized. Now it became desirable to learn as much as possible about the nature, behavior, and function of these bodies. Metz chose to approach this problem through study and comparison of chromosome behavior in organisms that diverge widely in their genetic and developmental behavior. Eminently satisfactory material was found in the “fungus gnats” of the genus Sciara. Using these Metz with his collaborators (especially H.V. Crouse), began a series of investigations.
In comparison with Drosophila and most other genetically known organisms, Sciara was found to deviate so widely as to reveal chromosome potentialities not foremly suspected, and to require revision of some supposedly well-established principles of chromosome behavior. Indeed, some processes were found which still defy explanation, especially in connection with sex determination, with interactions between chromosomes and cytoplasm in development and differentiation, and with the control and mechanism of chromosome movements in mitosis and meiosis. For example, in Sciara, the males produce only one kind of sperm, all of which carry two sister sex (X) chromosomes. the sex of the offspring is then determined, after intervening events, by an accurate process of elimination, which removes either obth of these sister chromosomes (in male production) or only one (in female production) from the somatic cells during development of the embryo. This process is influenced by the cytoplasm, which is preconditioned by the sex chromosomes of the mother (there are two types of mothers). Separations are thus made between three homologous X chromosomes - one from the mother, which not affected, and two sisters from the father. How can one of the two presumably identical sister chromosomes be thus influenced without the other and why are only the paternal ones affected? In the germ line an elimination also occurs, but by an entirely different process (as shown by the work of A.M. DuBois for the soma and R.O. Berry for the germ line). One of the two paternal sister X chromosomes is removed from all cells, in both sexes alike. The nature of the gonads is determined, not by the germ-line chromosomes, but by those of the somatic tissue (XX female, XO male).

Another example is seen in spermatogenesis. The expected random segregation of chromosomes does not occur. Instead, during a peculiar cell division process, all four chromosomes from the father move in one direction, their maternal homologs in the opposite direction. The former move backward in apparent opposition to forces that should typically tend to pull them forward. This behavior strongly suggests that chromosomes in general have a power of locomotion, acting but not manifest in ordinary mitosis. Direction of movement of chromosomes here is controlled by a mutational influence of sex of parent on each chromosome, regularly reversible in successive generations. The chromosomes which go backward did just the opposite in the preceding generation. Males in Sciara transmit only the chromosomes derived from the mother. Metz and his collaborators also found Sciara very favorable for other types of work, including studies on the giant salivary gland chromosomes. (This and the preceding references to Sciara do not take into consideration a peculiar type of chromosome found in some species of the organism and limited to the germ line).

Metz received his B.S. at Pomona College in 1911 and his Ph.D. at Columbia University in 1916. He was a staff member in the Carnegie Institution of Washington’s Department of Genetcs during 1914-1930 and Department of Embryology during 1930-1940, also acting as part time visiting professor at Johns Hopkins University in 1930-1937. In 1940 he became chairman of the Zoology department at the University of Pennsylvania, withdrawing from the chairmanship in 1955 to have more time for research. After his academic retirement in 1959, he continued research at the Marine Biological Laboratory in Woods Hole, Massachusetts. Metz was elected to the National Academy of Sciences in 1948 and to the American Academy of Arts and Sciences in 1951.