Functional-Genetical Mosaicism

The best known case of structural-genetical mosaicism is the Lyonization which was discussed in Chap. 1.3.3.2. This phenomenon is characterized by the formation of cell clones which differ in X chromosome activities. 

It has been demonstrated that lymphocytes do not differentiate if they are obtained from patients carrying the agammaglobulinemia mutation on the X chromosome. These cells have no y-globulin synthesis. Two populations of cells were observed in lymphocyte cultures from a woman patient heterozygous for the agammaglobulinemia mutation. Cells from one of these populations were able to differentiate and synthesize y-globulin. The second population of cells did not have this ability (Fudenburg and Hirschorn, 1964). 

Separate cases of differential expression of traits which are controlled by autosomal genes are known. In general, however, homologous autosomes have a synchronized activity. An illustration of this is the immunological data dealing with the allotypic specificity of cells of an immuno-competent tissue which was discussed previously. The clonal principle of differentiation in cells that produce antibodies is generally recognized (Papermaster, 1967 Burnet, 1971). 

It seems that the uneven distribution of ADH in the Malpighian tubules of Oregon R X Adh-nj hybrids was already determined when the enzyme activity first began to increase (the end of the first and beginning of the second larval stage). Thus, this increasing,enzyme activity is the first process which leads the biochemical mosaicism in third instar larvae (Korochkin et al., 1972 b). 

The heterogeneity of cell populations led to the realization of differential gene activity on the tissue level. The differences between cellular and tissue levels of differentiation can be illustrated when biochemical markers are used (Fig. 70). Suppose there are two electrophoretic variants of protein A (Aj-fast and A2-SI0W) which are controlled by a pair of alleles. Codominant expression will explain the presence of both electrophoretic variants in heterozygous individuals. This occurs at the cellular level. There is, however, a second possibility. There are cells which can synthesize only the Aj variant and cells which synthesize only the A2 variant. The proliferation of these cells will lead to clones. Therefore, these traits are also codominant at the tissue level. However, in each separate cell there is only one allele. 

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The surface activity of proteins (as well as many of their other functions) depends on the so-called tertiary structure of protein molecules, which is determined by the spatial arrangement of their polypeptide chains. This tertiary molecular structure depends in turn on the primary protein structure - the aminoacid sequence, which is determined by the genetic code of a cell. The surface of a protein globule is mosaic-like it contains both polar... 

The second category of the viral templates discussed here are spheroidal plant viruses, most of which have icosahedral symmetry. In this section, we first describe the fundamental characteristics of two representative viruses that have been widely enlisted cowpea mosaic virus (CPMV) and CCMV. We then discuss endeavors to functionalize the surfaces of these viral nanoparticles by both chemical and genetic modifications that mirror the ones utilized for TMV. Finally, efforts to harness a range of inner cavity sizes, perhaps the most unique feature of this class of viral assemblies, from various spheroidal viruses and protein cages for the synthesis of precisely controlled nanoparticles are described. 

In contrast to experimental malnutrition in animals, in which single nutrient deficiencies can be produced almost at will, human malnutrition is nearly always a mixture of abberations of different dietary constituents. Human PEM is in fact a mosaic of alterations in not only protein and energy nutriture, but in vitamin, mineral, and trace element balance as well. The problem is made even more complex by the impact of distinctive dietary intake patterns around the world, by the almost certain influence of genetics on cell function and response to stress of various kinds, and by the effect... 

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