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An Overview of Parasite Diversity
Published in Eric S. Loker, Bruce V. Hofkin, Parasitology, 2015
Eric S. Loker, Bruce V. Hofkin
Other examples of the disparity between existing taxonomy and the revelations of molecular phylogenetics are more glaring. For example, in the phylum Myxozoa, spore structure is a major feature differentiating taxonomic groups. The existing taxonomic scheme does not match the relationships derived from phylogenetic studies of either SSU rRNA or elongation factor 2 (EF-2) genes. This disparity is probably because relatively few characters are available to describe the myxozoan spore and because some spore configurations are just more successful than others. The result is that species that differ genetically have converged to the same spore morphology; that is, they exhibit homoplasy. Homoplasy refers to similarities that result from convergent evolution rather than common ancestry.
An Overview of Parasite Diversity
Published in Eric S. Loker, Bruce V. Hofkin, Parasitology, 2023
Eric S. Loker, Bruce V. Hofkin
It should by no means be concluded that morphological characters are inevitably misleading in attempting to define parasite diversity. Our taxonomic hierarchies have for decades been constructed using morphological criteria and many have proven to be robust. Morphological characters often provide convenient ways to identify species and can be used in conjunction with results from molecular studies to identify traits called synapomorphies, which are shared exclusively by members of a monophyletic group and the group’s immediate common ancestor. A monophyletic group is one that includes only taxa derived from a most recent hypothetical common ancestor of that group. One good example of the complementary use of molecules and morphology is provided by monogeneans of the genus Cichlidogyrus from African cichlid fish. These flukes are ectoparasitic flatworms living on the gills of the fish. Trees based on sequence data corroborate that characteristics of the haptor (the posterior attachment organ of monogeneans) provide reliable information about main lineages of monogeneans whereas morphological differences in reproductive organs are better for delineating among closely related species. The combined analysis of sequence data and morphological traits also helps to reveal homoplasy, referring to similarities resulting from convergent evolution rather than common ancestry. Homoplasy is likely to be a common outcome in parasite evolution because parasites often experience similar hosts and microhabitats within those hosts that favor the evolution of similar traits. Myxozoans seem to exemplify this issue. Our best understanding of parasite diversity will continue to derive from information from as many sources as possible, including both morphology and molecules.
Successful production of human epidermal growth factor in tobacco chloroplasts in a biologically active conformation
Published in Growth Factors, 2023
Yunpeng Wang, Jieying Fan, Niaz Ahmad, Wen Xin, Zhengyi Wei, Shaochen Xing
The plasmid pWX-Nt02 was introduced into tobacco leaves by biolistic bombardment. Transplastomic plants were regenerated on selective regeneration medium containing 500 mg L−1 of spectinomycin (Figure 1(B–D)). Several spectinomycin-resistant lines were obtained which were then screened by using primers for the presence of EGF, aadA and smGFP sequences (Figure 2(B)). The selected lines were purified to homoplasmy by giving 2–3 additional regeneration rounds of selection. The homoplasy was determined by amplifying the trnI-trnA intergenic region of the chloroplast genome (Figure 2(C)). The amplification of a fragment of 4.2 kb in tested lines confirmed the integration of transgenes at the chosen location on the chloroplast genome (Figure 2(C)). The presence of a single band approximate 4.2 kb in transplastomic plant line B21, J4 and J214 indicates that most of the chloroplast genome copies were transformed. The amplification of a smaller fragment (∼1.2 kb) in J213 line equal to that of wt shows the presence of untransformed copies of the plastome, and hence the line was still heteroplasmic. The PCR results were validated by Southern blot analysis using the trnI-trnA intergenic region from the wt tobacco chloroplast genome as a probe (Figure 2(D)). Eco RI was used to digest the ptDNAs before the Southern blot analysis and an approximate 7.5 kb specific fragment was expected for the recombinant ptDNAs, whereas 4.5 kb fragment was expected for the wt ptDNAs (Figure 2(A,C)). The results were accordant to those of the PCR analyses that all the tested lines except J213 were homoplasmic (Figure 2(D)).
Alu elements within the human major histocompatibility class I region in the Comoros Islands: genetic variation and population relationships
Published in Annals of Human Biology, 2019
Said Nassor Abeid, Majida Motrane, Hamid Farhane, Nourdin Harich
The advantageous characteristics of the Alu elements in human population genetics studies have been thoroughly reviewed by several authors (Batzer et al. 1996; Batzer and Deininger 2002; Romualdi et al. 2002; González-Pérez et al. 2010). In fact, Alu insertions are homoplasy free (identity by state and also by descent), their ancestral state is known (lack of insertion) and they are free from back mutation.