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Initiation of nucleolar organizer region (NOR) activity was observed by using the silver staining method at various times after activation or stimulation of differentiated cells. Two methods were used: (1) activation of human lymphocytes by treatment with phytohemagglutinin (PHA), and (2) cell-cell fusion of chick erythrocytes with squirrel monkey cells. An increase in NOR activity in lymphocytes was seen as early as 4 h after PHA treatment and between 10 and 22 h in the chick erythrocytes after fusion. In both systems, as the size of the dormant cell nucleus increased, the amount of silver staining increased until the silver-stained area approached that of cycling cells.

Chromosomal banding analyses have revealed two nonhomologous pericentric inversions in the telocentric group of chromosomes of a squirrel monkey, Saimiri sciureus. This individual is probably an intersubspecific hybrid whose parents originated from different geographical locations. The C-banding pattern shows polymorphism in location and amount of constitutive heterochromatin in at least four pairs of chromosomes. Ammoniacal silver (Ag-AS) staining specific for locating the nucleolar organizers indicates that these are located on only one pair of chromosomes and that there is a difference in the size of the nucleolus organizer regions between the homologs of this pair.

Cytological analysis of a squirrel monkey indicates a considerable degree of chromosomal polymorphism. DNA synthetic patterns reveal late synthesis in chromosomal segments that are C-band negative and asynchrony in DNA replication between homologs. Location of a satellite DNA with a CsCl neutral buoyant density of 1.691 g/ml was mainly in the noncentromeric constitutive heterochromatin.

Direct application of some common food seasonings, and of solubilized filtered extracts of these seasonings, has toxic effects on cells in culture. Asynchronous populations of several mammalian cell strains were grown in media containing one of the three food seasonings, cayenne pepper, curry and paprika. The cells exhibited decondensed and banded metaphase chromosomes. The spice turmeric arrested mitosis, altered chromosome morphology and interfered with nucleic acid synthesis. The metaphase chromosomes showed a progression of changes including uncoiling, chromatid separation, fragmentation and disintegration. This progression was dose- and time-dependent. Monitoring of the cell cycle using autoradiographic techniques suggested that turmeric interfered with cell-cycle progression. The rate of incorporation of [ 3 H]thymidine and [ 3 H]uridine was reduced to less than 25% of control values within 30 min when turmeric (10 μ g/ml) was added to asynchronous Chinese-hamster cells.

£A standard G-band karyotype is proposed for the genus Peromyscus. G-banded chromosomes of Peromyscus boylii glasselli (NF = 56), numbered and arranged according to euchromatic lengths, serve as the standard. It is suggested that rearrangements of the standard pattern which occur in other species of Peromyscus be described using the general methods of the Paris Conference (1971).

Improved techniques for culturing avian tissue in combination with a trypsinurea chromosome banding technique has allowed an analysis of chromosome homology in three bird species. Three macrochromosomes of the domestic chicken (Galliformes) showed homology with those of the ring-necked dove and the domestic pigeon (Columbiformes). The ring-necked dove and domestic pigeon displayed similar banding patterns, except that the pigeon possessed an additional four pairs of microchromosomes, which are fused to form two pairs of macrochromosomes in the dove. Both G- and C-banded metaphase chromosomes of the three species are presented, and chromosome evolution and phyletic relations are discussed.