Showing papers in "The Quarterly Review of Biology in 1962"

Phase Change in Higher Plants and Somatic Cell Heredity

Abstract: Phase change sometimes involves a relatively abrupt switch in potential of apical meristems in higher plants from a juvenile to an adult type of growth. The two growth forms are highly persistent in different parts of the same individual and in clonally propagated offspring. Reversion to the juvenile condition occasionally occurs in buds on adult-type shoots, and invariably takes place in sexual reproduction. It is pointed out that counterparts of phase change, expressed in a wide variety of ways, are common among both plants and animals; structures arise in the development of all organisms with characteristics that are not merely functional adaptations but are innate and self-maintaining in mitosis. Phase change is to be considered, therefore, as illustrating a general aspect of cell heredity and variation; it is singular only in the distinctness with which the alteration in type of growth may be phenotypically expressed. The mechanism whereby such characteristics are maintained and perpetuated in somati...

On the X chromosome of man.

Abstract: The history of our knowledge of the X chromosome of man is reviewed with appropriate reference to the contributions made through study of other forms. It is noteworthy that sex-linkage was first observed in man. X-linkage has been established for about 60 traits in man. Unlike a majority of autosomal traits in man, most of the observed X-linked traits are recessives (or incomplete recessives). The genetic map of the X chromosome is known only in the most sketchy manner but is likely to be filled in rapidly in the next few years through the use of newly discovered markers, such as the Xga blood group, and cytogenetic investigations of cases of X chromosome anomalies. It appears that the color-vision locus (or loci) is on the short arm and may be rather far from the kinetochore. Based on chiasma counts of autosomes, estimates of the genetic length of the X chromosomes are of the order of 100 map units (1 morgan). Independent segregation of color blindness and night blindness, of color blindness and hemophil...

The Origin of the Amphibia

Abstract: The origin of land vertebrates is a constant subject of discussion. Recent findings in zoology and paleontology (Latimeria, Ichthyostega, Hesperoherpeton, etc.) have supplied many new arguments, but the results arrived at by various authorities show considerable differences. The author is convinced, however, that present knowledge concerning the evolution of tetrapody can be arranged in a harmonious picture. This is the aim of the review. It is concluded that all the evidence speaks in favor of a monophyletic origin of land vertebrates. Among them, the important differences between amphibians on the one side and the reptiles and their descendants on the other are emphasized. The probable sequence with which the various tetrapod features have accumulated, the reasons which prevented the emergence of terrestrial forms from fishes from being ever repeated, and the evolution of the amphibian ontogeny are discussed.

The demography of frogs and toads.

Abstract: Quantitative studies of natality, mortality, and age-distributions of anuran populations are reviewed Specific problems involve estimates of (1) the age of individuals, (2) age-specific fertility, (3) natality of populations, (4) larval survival, and (5) age-specific post-metamorphic survival Some possible differences in the comparative demography of north temperate and neotropical anurans are suggested

Hybrid Sterility as an Isolating Mechanism in the Genus Drosophila

Abstract: Hybrid sterility is defined as the inhibition or suppression of the reproductive capacity of F1 or later generation hybrids between genetically different strains or populations, usually belonging to different species. It is a reproductive isolating mechanism which functions to prevent the exchange of genes between populations. Within the confines of the genus Drosophila there exists abundant hybrid material, even the crucial borderline cases between races and species, with which one may probe the problems of the bases of hybrid sterility (genic, chromosomal, cytoplasmic) and those of the origin and reinforcement of hybrid sterility (as a byproduct of genetic divergence, or via natural selection operating to prevent the production and reproduction of ill-adapted genotypes or both).

The organization, ontogeny, and orientation of the cestoda

Abstract: Consideration of the organization, ontogeny, and orientation of tapeworms, and comparison with the structure and development of other invertebrates, support the opinion that the cestode is an individual rather than a colony and that the transformation of the oncosphere to a procercoid or cysticercoid is a true metamorphosis in which there is a reversal of the antero-posterior axis. T EAPEWORMS have been known for thousands of years, and the ancients believed that both the segmented and bladder-worm stages arose spontaneously in the bodies of other animals. In the middle of the last century, Kiichen

Cellular chemotropism and chemotaxis.

Abstract: Chemotropism and chemotaxis have been demostrated in a variety of vegetative and reproductive cell types in both higher and lower plants and animals. None of the naturally occurring chemotropic or chemotactic agents, nor the mechanisms of their action, have been identified. Nevertheless, certain common characteristics can be noted. Based on parallels which have been observed in various instances of chemotropism and chemotaxis, as well as on mechanisms of action which have been proposed, some suggestions are made regarding potentially useful areas of futher investigation into problems of mechanisms and of comparative physiology of chemotropic and chemotactic substances.