China
Africa
Explore chapters and articles related to this topic
Repeated DNA Sequences and Polyploidy in Cereal Crops
Published in S. K. Dutta, DNA Systematics, 2019
In rye, wheat, and barley the repeating unit of rDNA is 9 to 10 kb in length.60 A significant fraction of the rDNA in these species is located in the C-band proximal to the secondary constriction of mitotic chromosomes.60 A diagrammatic representation of the rDNA repeating units is given in Figure 4. The two subclones (130.6 and 130.8) representing the tandemly repeating units of spacer region of rDNA have been sequenced.61
A History of Mental Retardation
Published in Merlin G. Butler, F. John Meaney, Genetics of Developmental Disabilities, 2019
Giovanni Neri, Francesco D. Tiziano
In 1969, Lubs (63) reported on a marker X chromosome, characterized by a secondary constriction near the end of the long arm, in the affected males of an XLMR family. Retrospectively, it turned out to be the first example of a chromosome fragile site, and it was destined to identify the most common XLMR condition, the fragile X syndrome. The emergence of this condition, with its relatively high prevalence and peculiar association with a chromosome fragile site, attracted considerable interest in the field, which in turn facilitated the discovery of the responsible gene, FMR1, in 1991 (64). This can be considered a significant date in the history of genetics, not only of the genetics of mental retardation, because the mutation of FMR1 is the first example of an unstable mutation, soon to be followed by several others. Work on other forms of XLMR has also been intense in recent years, leading to the tentative identification of more than 200 genes, several of which have already been cloned (65). A more detailed account of the history of XLMR was recently published by Neri and Opitz (66).
Benzene Carcinogenecity
Published in Muzaffer Aksoy, Benzene Carcinogenicity, 2017
Erdoǧan and the present author139 performed cytogenetic studies in 10 leukemic and 10 pancytopenic patients with chronic exposure to benzene. The results concerning the leukemic patients are summarized in Table 7. Numerical changes were found in five leukemic patients (polyploidy in two, trisomy C in two and monosomy C in one). Aberrations, such as acentric fragments, achromatic lesions, secondary constrictions, and dicentric breaks, were observed in nine patients. Among the findings observed in this study, the following are suggestive of leukemia: trisomy C, hypodiploidy (monosomy C), and the Ph chromosome (in a case of preleukemia). Interestingly, the Ph chromosome was observed by Erdoǧan and the present author in a case of leukopenia due to chronic exposure to benzene for 4 years without the signs of leukemia.139 After a 4-year period of nonexposure, these chromosomal aberrations disappeared. The other cytogenetic findings of these series are probably nonspecific. Table 5 (in Chapter 5) also show great variations in the severity of chromosomal aberrations obtained in ten patients with pancytopenia with chronic benzene toxicity.139-141
Use of argyrophilic nucleolar–organizer region-associated protein synthesis in skeletal muscle cells for prediction of chronic carbon monoxide exposure
Published in Toxin Reviews, 2020
Harun Gunes, Ayhan Saritas, Recep Eroz, Serdar Colakoglu
Nucleolar–organizer regions (NORs) are genetic loci located on the secondary constriction of acrocentric chromosomes (chromosomes 13, 14, 15, 21, and 22) in humans. NORs are formed by ribosomal DNA (rDNA) and proteins (Trere 2000). They are transcribed into ribosomal RNAs (rRNA) which are converted to pre-ribosomes in the nucleolus and join mature ribosomes in the cytoplasm (Hernandez-Verdun 2006). Active NORs can be stained with Silver nitrate (AgNO3) via the precipitation of metallic silver granules in the interphase. Activity status of NORs closely correlates with the amount of these granules (Jimenez et al.1988). Silver binds with non-histone-associated proteins which are transcriptionally active or transcribed and still having residual rRNA. Those proteins are called argyrophilic NOR (AgNOR)-associated proteins due to their silver affinity (Trere 2000).