Cytogenetic studies of Haplopappus gracilis in both callus and suspension cell cultures

Summary Investigations have been carried out on karyotype change in both callus and suspension cell cultures of Haplopappus gracilis (2n=4). It has been found that polyploidization arises directly in culture to give up to six times the normal diploid chromosome number in some cultures. In polyploid cultures, both chromosome loss and chromosome rearrangements occur to give rise to aneuploid karyotypes displaying chromosomes which differ in morphology from the diploid set. Whole or partial chromosome loss has been observed in the form of lagging chromosomes and chromosome bridges at anaphase, and micronuclei, ring chromosomes and chromosome fragments at other stages in mitosis. C-banded preparations have confirmed the occurrence of chromosomal rearrangements. Comparative investigations suggest that (i) more polyploidy occurs in callus cultures than in suspension cell cultures, and (ii) the presence of cytokinin (kinetin) in the culture medium may reduce the extent of karyotype change.     

Reactions of zoo visitors to free-ranging monkeys

This study assessed the potential of two types of primate exhibit both for enhancing zoo visitors' interest, knowledge, and enjoyment and for promoting conservation education. Visitors' reactions to a free-ranging group of cotton-top tamarins were compared with their responses to caged tamarins in three ways: 1) timing how long visitors spent at each exhibit, 2) recording the comments made by visitors about the exhibits, and 3) asking visitors to respond to questionnaires about the two exhibits. The results showed that the free-ranging group of tamarins provoked wider comment from members of the public than caged groups and that visitors were willing to spend much more time looking for and watching monkeys in trees than monkeys in cages. Visitors felt that improvements in the animals' welfare were obtained from allowing them to live free in the trees, thought that they could learn more from such groups than from caged animals, and enjoyed seeing the free-ranging tamarins more than the monkeys in cages. These results suggest that developing more naturalistic zoo exhibits can have considerable benefits not only for the animals involved, but also for public education in conservation issues. © 1994 Wiley-Liss, Inc.     

Phylogenetic diversification of immunoglobulin genes and the antibody repertoire

Immunoglobulins are encoded by a large multigene system that undergoes somatic rearrangement and additional genetic change during the development of immunoglobulin-producing cells. Inducible antibody and antibody-like responses are found in all vertebrates. However, immunoglobulin possessing disulfide-bonded heavy and light chains and domain-type organization has been described only in representatives of the jawed vertebrates. High degrees of nucleotide and predicted amino acid sequence identity are evident when the segmental elements that constitute the immunoglobulin gene loci in phylogenetically divergent vertebrates are compared. However, the organization of gene loci and the manner in which the independent elements recombine (and diversify) vary markedly among different taxa. One striking pattern of gene organization is the "cluster type" that appears to be restricted to the chondrichthyes (cartilaginous fishes) and limits segmental rearrangement to closely linked elements. This type of gene organization is associated with both heavy- and light-chain gene loci. In some cases, the clusters are "joined" or "partially joined" in the germ line, in effect predetermining or partially predetermining, respectively, the encoded specificities (the assumption being that these are expressed) of the individual loci. By relating the sequences of transcribed gene products to their respective germ-line genes, it is evident that, in some cases, joined-type genes are expressed. This raises a question about the existence and/or nature of allelic exclusion in these species. The extensive variation in gene organization found throughout the vertebrate species may relate directly to the role of intersegmental (V<==>D<==>J) distances in the commitment of the individual antibody-producing cell to a particular genetic specificity. Thus, the evolution of this locus, perhaps more so than that of others, may reflect the interrelationships between genetic organization and function.      

Interaction of purified DNA with plant protoplasts of different cell cycle stage: The concept of a competent phase for plant cell transformation

Summary The polycation mediated attachment of purified tritiated DNA to plant protoplasts has been measured by quantitative microautoradiography. The automated grain counting technique used, also provides information on the cell cycle stage of individual protoplasts, which circumvents the need to synchronize the plant cell population before preparation of protoplasts. With protoplasts from asynchronously dividing suspension cultures of Nicotiana syhestris (NS-1), S-phase protoplasts appear to be inefficient binders of ³H-DNA, as compared with G₁ or G₂ protoplasts. Protoplasts derived from a tumour line of Crepis capillaris (CAPT) exhibit ³H-DNA binding at all cell cycle phases, but Sphase protoplasts appear to be preferential binders. These differences are discussed with reference to cell cycle kinetics, membrane charge variation and the possibility of increasing the efficiency of genetic transformation of higher plant cells in culture.