The Cell in Development and Heredity

We may not be able to make you love reading, but animal cytology and evolution will lead you to love reading starting from now. Book is the window to open the new world. The world that you want is in the better stage and level. World will always guide you to even the prestige stage of the life. You know, this is some of how reading will give you the kindness. In this case, more books you read more knowledge you know, but it can mean also the bore is full.

Animal cytology and evolution

Publisher Summary This chapter discusses the physiological aspects of tumor formation in interspecies hybrids. An interspecific incompatibility in some crosses of Bryophyllum and of Gossypium leads to tumorous growth of hybrid shoots. Neoplasia can affect practically all plant organs besides the roots and shoots. Genetic studies on these plants have shown that tumor expression is controlled in inheritance by a single dominant gene (Frs) from L. chilense, which is often deficient in transmission. Tissue culture studies have shown that genetically tumorous and nontumorous segregants of tomato can be distinguished by their growth patterns in various culture media supplemented with nutrients and phytohormones. Tumor formation in these hybrids usually occurs at a mature stage in plant development but can be accelerated or repressed by chemical treatment. The physiological and biochemical processes underlying tumorigenesis are reflected in the persistent activation of normally repressed biosynthetic systems. The enhanced activity of growth factors, enzymes, and cell metabolites in tumorous plants and tissues provides evidence for an increased biosynthetic capacity in neoplastic cells.

Genetic Tumors: Physiological Aspects of Tumor Formation in Interspecies Hybrids

Karyology, the study of chromosomes, is now reaching a level of great detail. Recent studies have yielded a nearly complete knowledge of chromosome ultrastructure and now offer the possibility of interpreting in a reasonable way how the genetic information is organized on them, how it is duplicated, and how it is transferred to individuals of subsequent generations (Du Praw, 1970).

The Karyology of South American Primates and Their Relationship to African and Asian Species

A supernumerary microchromosome measuring 0.5–1 μm found in over half of the metaphases of a CREST scleroderma patient and his daughter has been characterized by various cytogenetic techniques. The microchromosome consisted of constitutive heterochromatin and contained nuclear antigens reacting with specific anti-kinetochore antibodies. The most remarkable property of the microchromosome was its non-random position: it was closely associated with the centromere of any of the normal chromosomes in the majority of the metaphases. Furthermore, an inordinately high rate of Y chromosome aneuploidy was found in the CREST scleroderma patient. The origin and structure of the microchromosome, its possible connection with the CREST variant of scleroderma, and the phenomenon of centromeric association are discussed.

Centromeric association of a microchromosome. A new category of non-random arrangement of metaphase chromosomes.

A synthesis of data in favour of a model of the superstructure of eukaryotic chromosomes is presented. The basic, independent features of the model are (1) the genetic material consists of one continuous DNA molecule which is coated with protein to form the chromosome; (2) various degrees of folding of the nucleoprotein fibre result in the different appearance of chromatin as euchromatin, heterochromatin, and entire chromosomes; (3) the haploid DNA is organized in a ring comprising all the chromosomes, which are connected by interchromosomal fibres; (4) specific segments of the basic chromosome fibre are organizer regions for attachment to the inner surface of the nuclear envelope. Data from electron microscopy, chromosome replication, partial chromosome pulverization, and the non-random distribution of chromosomes, induced claromosome damage and sister chromatid exchanges may be interpreted as evidence of chromatin/nuclear membrane organelles. It is suggested that the segregation of chromosomes in somatic cell hybrids may result from the lack of integration of the two different chromosomal superstructures, and that the breakdown of the superstructure may be the basis for the chromosome instability in tumor cells and other transformed cells. Clastogens may affect chromatin fibres particularly at their attachment to the nuclear membrane and induce a submicroscopic lesion in adjacent chromatids which may lead to exchange initiation. The deletion of part of a chromosome or the loss of one or more chromosomes may result from the formation of a smaller ring, which is left out of the superstructure. A change of the character of a nuclear membrane attachment site will lead to a change in chromosome morphology.

Superchromosomal organization and its cytogenetic consequences in the Eukaryota

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Superchromosomal organization and its cytogenetic consequences in the Eukaryota