100 MCQs from Dr. David Browne and Colleagues
David Browne, Selena Morgan Pillay, Guy Molyneaux, Brenda Wright, Bangaru Raju, Ijaz Hussein, Mohamed Ali Ahmed, Michael Reilly in MCQs for the New MRCPsych Paper A, 2017
Meta-analysis of genetic data in IMpACT has so far focused mainly on established ADHD genes from studies in children. The gene encoding the dopamine transporter DAT1, a regulator of signalling through the neurotransmitter dopamine in the brain, has been studied multiple times. Though results have been inconsistent for single genetic variants, a combination of genetic variations at two positions of the gene seems to increase ADHD risk in children. However, in a recent study of 1440 patients and 1769 controls in IMpACT, a different combination of variants at the same two positions was found to increase the risk for the persistent adult form of ADHD. This shows that age is an important factor to be taken into account in genetic association studies in ADHD and might explain some of the discrepancies in earlier studies. Transposons are sequences of DNA that can transpose into new positions in the genome of a single cell. (29)
Proteus
Dongyou Liu in Laboratory Models for Foodborne Infections, 2017
A traditional tool that allows for the identification of gene functions is random transposon mutagenesis. The basis of this technique is in the generation of mutant libraries that harbor a transposon insert, which abolishes the function of the affected gene. Transposons are mobile genetic elements that can move within the genome and can affect the function of gene expression. One of the limitations in identification and separation of nonvirulent mutants from a pool of mutants is that it is time consuming. In P. mirabilis, there are many studies that report the use of this technique. Recently, Holling et al. [55] used random transposon mutagenesis to identify genes involved in biofilm formation. They used a mini-Tn5Km2 transposon that was introduced into the wild-type P. mirabilis strain B4 by conjugal transfer from the donor organism, Escherichia coli S17.1λpir (Table 24.1). The mutants were screened by the crystal violet microtiter plate assay to identify bacterial impairment in catheter blockage. The end adjacent to the transposon was sequenced in order to identify the mutated gene.
Genetics as a Tool to Understand Structure and Function
Peter M. Gresshoff in Molecular Biology of Symbiotic Nitrogen Fixation, 2018
I have previously mentioned, en passant, general methods of inducing mutations in bacteria and plant seeds by irradiations and chemical mutagens. However, the resulting mutants arise randomly so that the identification and isolation of specific phenotypes is laborious. In recent years, greatly simplified ways have been devised for induction and genetic localization of mutations. Foremost among these has been the discovery and development of transposons. These comprise a range of naturally occurring linear segments of DNA, varying from a few hundred to many thousands of nucleotides long and located in apparently silent regions of the chromosomes of prokaryotes and eukaryotes. They have the bizarre property of occasionally excising themselves spontaneously and "jumping" across the cytoplasm to insert not only into other regions of the same chromosome, but into other chromosomes, as well as into DNA viruses and plasmids in the cell. Insertion into a functional gene produces a fairly stable mutation, but the transposon can jump out again, usually leaving the gene intact as before.
Effects of ionizing radiation at Drosophila melanogaster with differently active hobo transposons
Published in International Journal of Radiation Biology, 2019
In the last time, TEs are treated as a possible formation mechanism of radiation effects (Yushkova and Zainullin 2014; Yushkova 2017). By the experimental and theoretical investigation data of TEs at Drosophila, the conditions of stress the optimal viability level of organisms is maintained by balance between TEs transpositions and natural selection against their detrimental effects (Pasukova et al. 2004). The common feature of transposons is normally a relatively low level of their copies in host genome (Souames et al. 2003). The distinctive feature of hAT-superfamily transposons is formation of short but TEs (Lorento et al. 2018). Natural populations of E-cytotype may include a degenerated (i.e. those who lost Xhol restriction sites) hobo sequences which differ from canonic hobo sequences by 10–20% (Simmons 1992). Today, the high sensitivity of hobo transposons to intracellular stress (hybrid dysgenesis, isogenization) is known (Blackman et al. 1987; Zakharenko et al. 2007). There is little information confirming their sensitivity to environmental influences (temperature, radiation, chemical mutagens).
An overview of sex and reproductive immunity from an evolutionary/anthropological perspective
Published in Immunological Medicine, 2021
Yoshihiko Araki, Hiroshi Yoshitake, Kenji Yamatoya, Hiroshi Fujiwara
So how did mammals acquire the placenta? The human genome (all the DNA on chromosomes) is composed of approximately 3 billion base pairs. However, only a small proportion of the genome actually encodes proteins (the structural genes). The remaining genome contains sequences called ‘transposons’ [21], some of which are thought to be derived from ‘retroviruses’ such as human immunodeficiency virus. This suggests that during viral infections throughout evolutionary history, viruses were incorporated into the chromosomes of the infected organisms and passed down to the next generation through assimilation. The placenta has a completely different shape depending on the species. One hypothesis is that genes derived from retroviruses, Peg10/Sirh1 and Peg11/Sirh2, were important in the evolution of placental development [22–24]. The diversity of placental form and function is thought to be the result of successive, independent events [25].
Transposon mutagenesis in oral streptococcus
Published in Journal of Oral Microbiology, 2022
Yixin Zhang, Zhengyi Li, Xin Xu, Xian Peng
Transposons are mobile genetic factors that can move within genomes through ‘cut and paste’ or copy mechanisms. A transposase encoded by a transposon can recognise specific inverted repeat sequences at both ends of the transposon, separate the transposon from adjacent sequences, and insert it into a DNA target site [31]. The most common application of transposons is insertional mutagenesis, which can be used to create libraries of mutant strains. The success of transposon mutant library screening depends on the number of mutants screened and diversity of the library.
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