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The Scientific Basis of Medicine
Published in John S. Axford, Chris A. O'Callaghan, Medicine for Finals and Beyond, 2023
Chris O'Callaghan, Rachel Allen
The human genome organises our entire genetic information into a set of 46 chromosomes, which segregate our DNA for storage or transcription. Humans have 23 pairs of chromosomes, with one set inherited from each parent. These include 22 pairs of standard chromosomes and one pair of sex chromosomes (XX in females, XY in males). In the absence of transcription or replication, DNA is packed into chromosomes as chromatin with DNA wrapped tightly around very many nucleosome cores. The most densely packed form, heterochromatin, has a closed structure to maintain genes in a transcriptionally inactive state. In contrast, genes that are being expressed in order to produce protein are located within open euchromatin, to allow access for the necessary transcriptional machinery.
Genetics and exercise: an introduction
Published in Adam P. Sharples, James P. Morton, Henning Wackerhage, Molecular Exercise Physiology, 2022
Claude Bouchard, Henning Wackerhage
Chromosomes have two arms and a central constriction which is termed the centromere. The short arm of a chromosome is denoted as p and the long arm as q. Each arm of the chromosome is subdivided into regions numbered consecutively from the centromere to the telomere which is the tip of each chromosome arm. Each band (i.e. the dark and light stripes of a chromosome seen in Figure 3.5) within a given region is identified by a number. With this nomenclature, it is possible to specify any chromosomal region by its “cytological address”. For example, chromosome 1 is composed of about 249 million (mega, M) DNA base pairs (Figure 3.6). 1p22 refers to chromosome 1, p arm, region 2, band 2. Since the sequence of the DNA bases of the entire human genome is now available, it is possible to specify a physical position on a given human chromosome in terms of the exact base number in a sequence ranging from one to millions. For instance, there are 4,300 genes encoded on chromosome 1. The gene KIF1B which encodes kinesin family member 1B codes for a motor protein that transports vesicles within cells. It is located on 1p36.22 and extends from 10.21 to 10.38 M bases of DNA.
Molecular Biology and Gene Therapy
Published in R James A England, Eamon Shamil, Rajeev Mathew, Manohar Bance, Pavol Surda, Jemy Jose, Omar Hilmi, Adam J Donne, Scott-Brown's Essential Otorhinolaryngology, 2022
A gene is a region of the chromosomal DNA that produces a functional ribonucleic acid molecule (RNA). It comprises regulatory DNA sequences that determine when and in which cell types that gene is expressed; exons are coding sequences and interspersed introns are non-coding DNA sequences.
Self-reported effects of perceived social support on marital quality in balanced translocation patients and their spouses undergoing preimplantation genetic testing in China: actor–partner interdependence model
Published in Journal of Obstetrics and Gynaecology, 2022
Fengyi Mo, Xiaorui Hu, Qing Ma, Li Zhang, Lanfeng Xing
Chromosomal abnormalities, one of the most frequent causes of genetic diseases (Mierla et al. 2015), are defined as a genetic disease caused by abnormalities in the number, morphology or structure of chromosomes, often resulting in miscarriage, congenital mental retardation, mental retardation and multiple malformations (Chen et al. 2020). The most frequent chromosomal abnormalities are balanced chromosomal rearrangement, sex chromosomal mosaicism and inversion. The rate of a chromosomal anomaly in the general population is 0.37–1.86%; however, the rate in patients with a history of adverse pregnancy is 3.95–14.3% (Liu et al. 2013). Chromosomal abnormalities cannot be treated medically since they are irreversible (Chen et al. 2020). Balanced translocation is a situation in which both breakage and reconnection of chromosomes occur at abnormal positions, including both Robertsonian and reciprocal translocations. Approximately, 0.5–5% of couples with reproductive problems carry a balanced translocation (Munné et al. 2000; Findikli et al. 2003). However, at present, the specific mechanisms underlying balanced translocation remain unclear (Chen et al. 2020).
Differences in foot dimensions between children and adolescents with and without Down syndrome
Published in Disability and Rehabilitation, 2022
Nirmeen M. Hassan, Andrew K. Buldt, Nora Shields, Karl B. Landorf, Hylton B. Menz, Shannon E. Munteanu
Down syndrome is a common chromosomal abnormality that results in the trisomy of chromosome 21 [1]. It is associated with a number of orthopaedic anomalies and musculoskeletal disorders [2]. Approximately 20 to 27% of people with Down syndrome experience musculoskeletal disorders, and foot deformities make up 30% of all reported orthopaedic complaints [3]. Structural anomalies such as hallux valgus deformity and flat feet are the two most commonly reported in the literature [4–6]. However, other structural anomalies that may cause foot problems include digital deformities, bony deformities of the forefoot [4], hallucal cleft, isolated calcaneal valgus [4] and a plantarflexed first ray. Several of these structural anomalies are thought to occur secondary to higher body mass index [7], muscular hypotonia [8], ankle instability [9] as well as ligamentous laxity [10] – all of which are associated with Down syndrome. These structural anomalies may have a negative impact on gait, engaging in daily activities [11] and footwear-fitting.
Analysis of an NGS retinopathy panel detects chromosome 1 uniparental isodisomy in a patient with RPE65-related leber congenital amaurosis
Published in Ophthalmic Genetics, 2021
Fabiana Louise Motta, Rafael Filippelli-Silva, Joao Paulo Kitajima, Denise A. Batista, Elizabeth S. Wohler, Nara L. Sobreira, Renan Paulo Martin, Juliana Maria Ferraz Sallum
Gene panel sequencing analysis allowed the aforementioned hypotheses to be refuted or accepted. (i) In the absence of a paternity test, comparison of NGS data between the proband and his parents showed a similar number of chr2-22 variants inherited from his mother and the putative father. This is not compatible with the expected pattern of non-paternity. Chromosome 1 was excluded due to the odd mode of inheritance; (ii) A de novo mutation was rejected because 20 additional homozygous variants on chromosome 1 presented the same inheritance pattern as the RPE65 pathogenic variant, making the likelihood of 21 de novo events occurring simultaneously unlikely; (iii) The NGS raw data of the proband and his father suggested no gross deletion on chromosome 1, which was confirmed by the proband’s SNP array; (iv) The trio NGS analysis showed the proband’s chromosome 1 did not present exclusively paternal inherited variants, unlike what was observed in other autosomal chromosomes. Furthermore, SNP array revealed three large regions of homozygosity on chromosome 1 intercalated by heterozygous segments, suggesting the hypothesis of isodisomy and heterodysomy, respectively. One of these homozygous segments encompasses the RPE65 gene and, thereby, the pathogenic causative variant. All other chromosomes were largely heterozygous, suggesting a biparental inheritance pattern. Therefore, NGS analysis together with SNP array reinforces maternal UPD.