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Genetics and exercise: an introduction
Published in Adam P. Sharples, James P. Morton, Henning Wackerhage, Molecular Exercise Physiology, 2022
Claude Bouchard, Henning Wackerhage
The DNA of the human genome is divided into 46 chromosomes. Normally, the chromosomes are dispersed within a nucleus and individual chromosomes cannot be recognized under the microscope. However, during the so-called metaphase period of cell division, DNA condenses to form tightly packed chromosomes (15) that segregate into two daughter cells. The human genome is composed of 22 pairs of non-sex chromosomes, termed autosomes, plus two sex chromosomes, which are XX in females and XY in males. Figure 3.5 depicts the chromosomes in a human cell.
Meiotic Abnormalities in Infertile Males
Published in Carlos Simón, Carmen Rubio, Handbook of Genetic Diagnostic Technologies in Reproductive Medicine, 2022
Mireia Solé, Francesca Vidal, Joan Blanco, Zaida Sarrate
The meiotic process is highly regulated, involving different cell control mechanisms (checkpoints) designed to detect anomalies in chromosome recombination and segregation. The recombination checkpoint prevents cells from overcoming this stage if chromosome pairing anomalies are present [2,17], and spermatogenic arrest at this stage has been associated with defects in recombination and/or in homologous chromosome synapsis [8,18]. The spindle assembly checkpoint regulates the transition from metaphase to anaphase and acts to retain cells at metaphase I or II until all bivalents or chromosomes are properly orientated to the spindle [19–21], which is a prerequisite for correct segregation.
Biological Effects and Medical Treatment
Published in Alan Perkins, Life and Death Rays, 2021
Measurement of the blood cell count is important and the level of blood lymphocytes, a type of white cell of the immune system, is one of the best indicators of the severity of radiation injury. A decrease in lymphocyte counts occurs promptly within 24 hours after radiation exposure. Radiation dosimetry may also be estimated based on chromosome analysis. A blood sample can be taken and the cells put in culture to stimulate the lymphocytes to grow and divide. Once they reach the point of cell division known as the metaphase stage, the chromosomes can be seen under a microscope (Figure 11.4).
Cytogenetic and molecular genetic methods for chromosomal translocations detection with reference to the KMT2A/MLL gene
Published in Critical Reviews in Clinical Laboratory Sciences, 2021
Nikolai Lomov, Elena Zerkalenkova, Svetlana Lebedeva, Vladimir Viushkov, Mikhail A. Rubtsov
Conventional karyotyping emerged as the first method of detection for chromosomal rearrangements after the description of normal mitotic human chromosomes in 1956 [28]. The technique improved significantly with the method for chromosomal banding, proposed in 1970 [29], representing the different densities of chromatin along each chromosome. The method principally consists of cell culture, harvesting metaphase plates, and chromosome staining (Figure 1). Chromosomal banding can be visualized by partial trypsin hydrolysis (G-banding [30]) or prolonged heating in phosphate buffer (R-banding [31]), followed by staining with azure-eosin dyes. The obtained samples are scoped with light microscopy, and specialized software can be applied for image analysis and storage (e.g. IKAROS by MetaSystems GmbH, Altlussheim, Germany). When analyzing metaphase plates, chromosomes are divided into pairs of homologs and compared with the normal karyotype. Chromosomal rearrangements are recorded according to An International System for Human Cytogenomic Nomenclature [32].
Genotoxic and mutagenic studies of teratogens in developing rat and mouse
Published in Drug and Chemical Toxicology, 2019
Eyyüp Rencüzoğulları, Muhsin Aydın
Micronucleus is a small nucleus that forms whenever a chromosome or a fragment of a chromosome is not incorporated into one of the daughter nuclei during the cell division. It is found outside the main nucleus and formed in telophase due to the acentric chromosomal or chromatid fractures. Also, it could be formed during the telophase from one or a few chromosomes or chromatids that lag behind the anaphase (anaphase bridge) (Surrallés et al. 1995). In addition, multipolar anaphase and telophase could cause MN formation (Topaktas and Rencuzogullari 2010). Chromosome loss or nondisjunction of chromosomes that may lead to MN formation is one of the important events that is observed in cancer and aging. This is probably the result of disruption in spindle apparatus and centromere or condensation of the chromosome prior to metaphase (Dellarco et al. 1985). Thus, both the clastogenic and the aneugenic effects can be determined by the MN test (Kirsch-Volders et al. 1997, Norppa and Falck 2003). In previous studies, the increase in MN frequency in peripheral blood lymphocytes from cancer patients was found to be as much as the MN frequency in the targeted cancer tissue (Cheng et al. 1996, Duffaud et al. 1997, Bonassi et al. 2007). In addition, in the study of Fenech et al. (1999), which have been conducted with an international collaboration, has clearly shown the relationship between MN and cancer in humans.
Emerging strategies to target the dysfunctional cohesin complex in cancer
Published in Expert Opinion on Therapeutic Targets, 2019
Konstantinos Mintzas, Michael Heuser
Sister chromatid cohesion is a fundamental process of the life cycle; it starts shortly prior to DNA replication and is maintained until anaphase, when the last remaining cohesin complexes are removed[9]. Cohesin complexes are assembled and recruited to DNA prior to DNA replication. At first, cohesin encircles one single chromatid; when the replication fork passes through that part of DNA, a single cohesin complex encircles both sister chromatids, thus providing the necessary cohesion for the following steps (Figure 1)[4]. During S and G2 phases, cohesion established by STAG1-containing complexes is necessary for successful replication of telomeres – complex regions that can stall the replication fork. When cells enter metaphase mainly STAG2-containing complexes coordinate the successful distribution of newly formed chromosomes in daughter cells. Sister chromatids are kept in close contact until the mitotic spindles of the microtubules attach to their centromeres. That way, all chromosomes are bi-oriented and mother and daughter centrioles are colocated[10].