David A. Hungerford

Computer-Oriented Analysis of Human Chromosomes. I. Photometric Estimation of DNA Content

The potential value of DNA content as a parameter for karyotype analysis is presented, and a method is developed based on optical density measurements of gallocyanin-chrome alum stained chromosomes. The optical information is obtained automatically in digital form by CYDAC, a special purpose cytophotometer. A partly automated computer analysis of the data then provides the relative stain content of individual chromosomes and chromosome arms. Experience with three metaphases from the same human female indicates stable clustering of the results, with sufficient discrimination among clusters to identify eleven discrete chromosome classes. It would appear from the values obtained that gallocyanin-chrome alum stain content of individual chromosome arms correlates closely with length and ultraviolet absorbance values given in the literature. It is not yet clear whether stain content represents DNA content alone, or includes other constituents of the chromosome that tend to be proportional to DNA content. Judging from the analysis of errors, improvement in the resolution of the photometric method can be expected. This approach has promising applications in the automation of karyotype analysis and as an additional and powerful parameter in cytogenetic study.

CHROMOSOME CHANGES IN HUMAN LEUKEMIA AND A TENTATIVE ASSESSMENT OF THEIR SIGNIFICANCE

In the five years since modern techniques of human cytogenetics first were applied to the study of leukemia,l#z a sufficient number of cases has been investigated to permit certain generalizations to be advanced concerning the types of chromosome change present in the common forms of this disease. We plan in this paper to summarize data from our own laboratories, published and unpublished, as well as the published data of others, and to advance what seem to be reasonable interpretations concerning the significance of these chromosome changes. Chronic granulocytic leukemia. This is the one form of human cancer which thus far has been shown to be characterized by a consistent and apparently specific chromosome change. In reports from four different l abora t~ r i e s ,~ -~ an abnormal small chromosome (designated the Philadelphia’ chromosome and abbreviated Ph’), has been described in the cells of nearly every case of typical chronic granulocytic leukemia. The Ph’ chromosome, a #21 chromosome with approximately half of its long arm missing, has not been found in cells other than those of the circulating blood and boi,e marrow,l and hence the change is apparently limited to the leukemic cells. It is not present in skin cells4 or in lymphocytes stimulated to divide by phyt~hemagglutinin,~ but its presence in erythroid and megakaryocytic cells, which may be involved in the leukemic process, has not been definitely ruled out.6 The Ph’ chromosome is present throughout the clinical course of chronic granulocytic leukemia. It has been demonstrated in the blood and bone marrow of two patients at the outset of the disease, before any clinical symptoms developed3, and IaoT; it can be readily observed in dividing marrow cells in patients in complete clinical remi~s ion;~ and it persists in the “blast crisis’’ which usually terminates the disease, although additional chromosome changes may be s~per imposed .~ ,~ Since the demonstration of the Phl chromosome requires the presence of dividing leukemic cells, it may not be observed in peripheral blood leukocyte cultures from patients in remission, in relapse with few circulating immature cells, or in the “blast” stage, if the circulating blasts fail to divide in culture. In these instances, the Phl chromosome can be observed in marrow cells. Failure to examine dividing leukemic cells undoubtedly accounts for some, but perhaps not all, of the few cases reported of typical chronic granulocytic leukemia without the chromosome abnormality. Of the 21 cases which we have examined to date, the only patient in which the Phl chromosome was not observed was in a blast crisis and bone marrow was not obtained.3 The etiology of the Phl chromosome is unknown. The aberration is of a type known to be caused by ionizing radiation (see discussion by Nowell and Hunger-

Uniformity of karyotypes in the Camelidae.

The Old World camels of the genus Camelus have diverged from the New World camels of the genera Lama and Vicugna over a period of more than a m

Artiodactyl Mammals: Their Chromosome Cytology in Relation to Patterns of Evolution

The orders Artiodactyla, Carnivora and Primates comprise the three most successful and the most widespread groups of large mammals. There are 9 living families of artiodactyls, in which are represented more than 190 species, including such forms as pigs, camels, deer, giraffe, antelopes, cattle, sheep, and goats. This order has long occupied much of the world’s land area, except for the oceanic islands and Australia. Even in the latter areas, some artiodactyls have been introduced by man. They are clearly the dominant plant-eating mammals of the present time.