Digitization has become part and parcel of the contemporary prosthodontics with the probability of most of the procedures being based on the digital techniques in near future. Let us think of X-rays or photographs, making impressions, recording jaw movements or fabricating prosthesis, educating and training new dentists or patient motivation for practice build up, all has become digital. CAD-CAM has revolutionized not just the ceramic technology but has also been used for the CAD-CAM implant surgeries, maxillofacial prosthesis and diagnostic splints. Today a practicing dentist needs to be abreast with the latest but with the technology changing so fast, this poses a great challenge. There is endless scope of digitisation and technology in prosthodontics- let it be in the clinical and lab procedures like use of CAD-CAM technology, stereolithography, rapid prototyping, use of virtual articulators and digital face bows, digital radiographs, or in the field of training, education and research by the use of virtual patient programs, dental softwares, optoelectronic recording of jaw motion, digital instron machine, retention testing device, audiovisual aids,… the list will remain endless. The article reviews those various aspects of prosthodontics where digitization has modified the conventional procedures. For discussion they have been considered under the educational aspect, diagnostics, treatment procedures, prosthesis fabrication and lastly the research and futuristic development. The day is not far when remote sensing robotic devices would be performing the restorations under the command and surveillance of the master-the dentist without his immediate presence.
Our investigation of 460 true-breeding lines confirms a long-standing observation that natural phenotypic and genetic variability in the diploid wheat Triticum monococcum L. is limited. The modes of inheritance of 12 morphological characters are discussed in light of the extensive information available on the genetics and cytogenetics of many of these characters in the related wheat Triticum aestivum. Analysis of data from appropriate crosses, complementation studies, and observations of phenotypes of F1s and F2s from crosses between lines expressing dominant traits indicate that each of these characters is determined by one major gene. A multiple allelic series exists at each of the Hg (glume pubescence) and Hn (node pubescence) loci. The genes for six of these characters fall into two closely linked groups. Genes Bg (glume colour) and Hg are the same distance apart as in Triticum aestivum, indicating that at least this segment of chromosome 1A has been highly or completely conserved since the origin of the polyploid wheats. The genes Sg (glume hardness), La (lemma awn length), Fg (false glume), and Lh (head type) are also very closely linked, with the outside markers being only 4 map units apart. The dominant and recessive alleles of genes determining these characters should serve as excellent markers for linkage and chromosomal mapping because of their complete penetrance and constant expressivity. Tentative assignments of genes and linkage groups identified in this investigation to specific chromosomes of T. monococcum have been made on the basis of known chromosomal locations of A genome genes in T. aestivum. The tentative assignments could be verified using a variety of genetic and cytogenetic approaches. It is suggested that a thorough study of the genetic heritage of einkorn wheat will require the use of induced mutants since natural genetic variability is low in this species.Key words: Triticum, characters, inheritance, linkage, mapping, A genome.
Electron microscopy of synaptonemal complex spreads from autotetraploid Triticum monococcum (2n = 4x = 28) revealed a minimum mean of 3.59 multivalents per zygotene–pachytene nucleus. The range of values was from 1 to 6 multivalents per nucleus. Most of the multivalents were quadrivalents with single, medially located pairing partner switch points. Lateral element pairing switches, particularly the few multiple switches, were often accompanied by extensive asynapsis around the switch point. The synaptonemal complex multivalent frequency is considerably higher than the metaphase I quadrivalent frequency previously reported for the same material. Calculations of expected pachytene quadrivalent frequency from metaphase I data, using several published theoretical models, gave values that did not agree with the results obtained here. The difference between the multivalent frequencies at pachytene and metaphase I does not appear to be the result of a correction process. Instead, it could be caused by a combination of preferential pairing or crossing-over and the effects of the position of partner switches and asynapsis associated with switches. Key words: autotetraploid, multivalents, synaptonemal complex, pairing effects.
Mature triploid seed from reciprocal (2n = 4x × 2n = 2x) crosses in Triticum monococcum was minute and shrivelled because of endosperm collapse and therefore failed to germinate. This necessitated the excision of embryos from successful pollinations and their growth in vitro to ensure subsequent germination so as to obtain viable and vigorous autotriploids. A comparison of these triploids with their diploid and tetraploid progenitors revealed that cell size, kernel weight, and pistil size increased with an increase in ploidy level. However, unlike other species, optimum expression was observed in these triploids for plant height, tillering, size of spikes, number of spikelets/spike, and leaf size. Earliness, althoughenhanced in tetraploids relative to diploids, was delayed in the triploids. Mean numbers of univalents, bivalents, and trivalents per microsporocyte were 2.65, 2.60, and 4.38, respectively. Only chains (93.5%), which formed V-shaped metaphase I (MI) configurations, frying pan (5.0%), and Y-shaped (1.5%) trivalent associations occurred. On the average, two reciprocal exchanges occurred per bivalent and trivalent. Trivalents corriented randomly at MI. At anaphase I, all sets of three homologues segreated randomly to the two poles, lagging univalents always divided equationally, and only meiocytes with such chromosomes formed micronuclei. The reasons for similarities and differences in meiotic behaviour of T. monococcum triploids with those of other species are discussed. Confirmation of the conclusions drawn with respect to the cytology of the triploids was obtained from similar cytological observations with primary single trisomics. These triploids produced euploids, primary single trisomics as well as some double and triple trisomics all of which differed phenotypically from diploids. Triticum monococcum, like most diploid species, is highly intolerant of aneuploidy. Possible reasons for the differences in levels of tolerance of aneuploidy in species like T. monococcum and those like Petunia hybrida, which are highly tolerant of aneuploidy, are discussed. Pollen fertility was high and seed fertility was very low. Reasons for the latter as well as the high fertility in species that are highly tolerant of aneuploidy and allotriploids are discussed.Key words: Triticum monococcum, autotriploid, trisomic, cytology, breeding behavior, fertility, morphology.
In situ hybridization with [3H]dCTP labelled pScT7 (5S rDNA) and pTa80 (18S + 26S rDNA) indicated that both hybridized to the terminal regions of two pairs of chromosomes in Triticum monococcum. When the hybridization was performed with a mixture of both probes, only two pairs of chromosome arms were labelled, which suggested that the loci of both genes were located in juxtaposition to one another. Both probes labelled one pair of sites more heavily than the other. Southern analysis of 5S with BamHI-digested DNA from 12 accessions of T. monococcum (including T. urartu) produced two superimposed ladders of approximate sizes of 500 and 330 bp, which differ from T. aestivum in which 500- and 420-bp ladders were found. The 500-bp ladder is derived from chromosome 5A (5SDna-A2) and the 330-bp ladder from chromosome 1A (5SDna-A1). The recognition site for SstI was present in the long spacer region but absent in the short spacer as in T. aestivum; however, unlike T. aestivum, there were HaeIII (GGCC) and HindIII (AAGCTT) recognition sites in the short spacer region. The TaqI recognition sites (TCGA) in the long and short spacer regions are probably more highly methylated in T. monococcum than in T. aestivum. The results have implications regarding the evolutionary changes that occurred in the A genome of the hexaploid compared with the diploid.
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