Cytogenetics / edited by Ronald L. Phillips, Charles R. Burnham.

Date:
[1977], ©1977
Catalogue details

Licence: Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0)

Credit: Cytogenetics / edited by Ronald L. Phillips, Charles R. Burnham. Source: Wellcome Collection.

    25/520 (page 3)
    Historical Perspectives J's, or rods. Several papers appeared in which line diagrams not designated by any special term were used to represent the chro¬ mosomes; for example, Hance (1918) for a trisomie (15-chromo- some) plant of Oenothera scintillans; Painter (1925) in a compara¬ tive study of the chromosomes of man and several other mam¬ mals; and Rüttle (1927) for one species of Nicotiana. Delaunay re¬ viewed the studies of external chromosome morphology in 1929. In 1931 two important papers by Lewitsky appeared. One dealt with the karyotype in systematics (1931). The other, from which ex¬ cerpts are reprinted in this volume, used line diagrams that he termed idiograms to represent lengths, centromere positions, and secondary constrictions of the chromosomes in a wide range of species including agronomic crop species. He made all his obser¬ vations on cells from sectioned material. He measured the somatic metaphase chromosomes by making trigonometric calculations from readings using the micrometer calibrations on the fine-ad¬ justment knob of the microscope. Although the text of the paper was published in both English and Russian, the diagrams illustrat¬ ing the calculations are only in the Russian text. With the develop¬ ment of smear techniques that flattened the cells, and additional refinements, idiograms have become even more important in chromosome studies of plants and animals. As an outgrowth of the idiogram idea, karyotypes are often displayed pictorially by cutting out mitotic metaphase chromosomes from a photomicrograph and arranging them by length and in pairs and aligned such that the centromeres are at the same level, and the short arms are oriented upward. This method of reporting karyotypes is almost always used for man and other animals and is becoming increasingly pop¬ ular for plants. Metaphase chromosomes, as observed in the early days, dis¬ played only limited cytological detail. McClintock's 1930 paper (Pa¬ per 2) demonstrated that the pachytene stage of meiosis in maize could be used to distinguish the different chromosomes and also to locate more precisely the breakpoint positions for chromosome translocations (interchanges). She had published (1929a) an idio¬ gram of the maize chromosomes based on their morphology at the first postmeiotic division in the microspores. Among the progeny of a triploid maize plant, she had established trisomies for many of the chromosomes. Since the n + ^ microspores from a trisomie plant had one chromosome in duplicate, she was able to identify that chromosome. She also determined its morphology at pachy¬ nema in the trisomie plant. She crossed the different trisomie stocks with genetic markers for the different linkage groups. At that time, trisomie plants were identified by chromosome counts 3