An Evaluation of Baum Et Al.'s Assessment of the Genomic System of Classification in the Triticeae

Abstract

We have critically evaluated Baum, Estes, and Gupta's (1987) assessment of the genomic system of classification in the tribe Triticeae. They have raised some valid concerns about basing a taxonomic classification on genome relationships. However, some of their objections are ill‐founded. Baum et al.'s contention that genome analysis can only supplement other criteria in assessing phylogeny is inaccurate. Genome analysis by itself has yielded extremely useful information on phylogenetic relationships in the Triticeae, and their assertion that an individual morphological trait be given the same weight as genomic relatedness is not tenable. Moreover, these authors have adopted cladistic algorithms in the Triticeae, an analysis appropriate only in groups where reticulation has not occurred. Evolution in the Triticeae is highly reticulate, the main sources of reticulation being allopolyploidy and homoploid recombinational speciation.

DC electrical resistivity studies and structure of Ni0.5Zn0.5CrxFe2-xO4 nanoferrites

“…Also, the presence of Cr 3+ ions in large number at the octahedral sites dilutes the possible formation of Fe 2+ and therefore electron hopping can be properly controlled which results in the decrease of electrical conductivity. 9 Another notable contribution to the observed increase in resistivity is due to the substantial decrease in the grain size from 0.303 µm to 0.156 µm on chromium substitution as shown in the Table 2. In general, the larger grains are surrounded with fewer grain boundaries as such the grain conduction predominates which contribute to electrical conductivity.…”

“…On the other hand, the Cr 3+ ions due to their stable oxidation state might possibly decrease the conduction mechanism between Fe 2+ ↔ Fe 3+ at the B-sites of the spinel lattice and thereby increasing the electrical resistivity. 9 Substitution of Cr 3+ ions of lower ionic radius in the place of Fe 3+ ions have resulted 8 in substantial structural modifications which possibly influence largely the electrical properties of Ni-Zn nanoferrite. Therefore, with reference to the reported results, 8 the present studies on the morphological, microstructural and DC electrical resistivity measurements of chromium substituted Ni-Zn nanoferrite sintered at 1000 • C synthesized by nitrate-citrate gel autocombustion method has been discussed.…”

Hybridizing Brassica rapa with wild crucifers Diplotaxis erucoides and Brassica maurorum

“…Both these reports, however, relied solely on the meiotic chromosome pairing data of the F 1 hybrids to draw inferences on the intergenomic affinities. Such data have a limited value for genome analysis (Jauhar and Crane 1989) as they fail to differentiate between the allo-and auto-syndetic pairing; hence they tend to inflate the affinity relationships. In the absence of competition for pairing partners in interspecific F 1 hybrids, even distantly related homoeologues may frequently engage in pairing.…”

Intergeneric crosses between Hordeum and North American Elymus (Poaceae, Triticeae)

“…Genome analysis is considered an important tool in determining relationships in the tribe Triticeae (STEBBINS and SNYDER 1956;DEWEY 1984;JAUHAR and CRANE 1989;WANG 1989), though some authors have raised theoretical objections (SEBERG 1989). Genomic affinity is determined by the chromosomal pairing behaviour in metaphase I (MI) of the meiosis, as expressed in intergeneric hybrids.…”