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Radiobiology of Normal Tissues
Published in W. P. M. Mayles, A. E. Nahum, J.-C. Rosenwald, Handbook of Radiotherapy Physics, 2021
Individuals have 23 pairs of chromosomes (one inherited from each parent) and therefore, two copies of every gene. If a person has a mutation in both copies, they are known as homozygotes. The syndromes listed in the previous paragraph are associated with homozygous mutations, and these are rare. More of us are heterozygotes, i.e. carrying one copy of a particular gene (and therefore, a mutation in just one chromosome). These tend to be carried in a recessive mode, i.e. without expressing the syndrome itself. Heterozygotes for a radiosensitivity gene do not show the same level of sensitivity as the homozygote (who carries two identical copies of a particular gene), but they may show a tendency towards increased radiation damage. When a heterozygote mutation is seen in a large proportion of a population (>1%), it is called a single nucleotide polymorphism (SNP). SNPs are the most common type of genetic variation between individuals. SNPs affect phenotypes (e.g. eye colour and height) and disease susceptibility. Many traits (e.g. eye colour and height) are termed polygenic; i.e. SNPs in multiple genes (hundreds) affect the trait, with each having a small effect but together, a large effect. Current studies are attempting to identify the genetic variants that influence radiation sensitivity and exploring tests that measure an individual patient's radiosensitivity (Barnett et al. 2012).
Genetics and metabolic disorders
Published in Jagdish M. Gupta, John Beveridge, MCQs in Paediatrics, 2020
Jagdish M. Gupta, John Beveridge
By definition autosomal recessive disorders are not manifest in the heterozygote. Generally, autosomal recessive conditions affect only members of the one sibship and affected individuals are not usually seen in earlier or subsequent generations. Consanguinity is more commonly seen amongst the parents of the very rare autosomal recessive disorders, where meeting a carrier by 'chance' is less likely. If both parents are heterozygous the risk is 1 in 4 for each offspring. Affected persons married to homozygous normal individuals will produce carrier individuals only and none of their offspring will be affected. Homozygous affected individuals produce only affected offspring unless the abnormality is due to mutations within different genes.
An Approach to Inherited Pulmonary Disease
Published in Stephen D. Litwin, Genetic Determinants of Pulmonary Disease, 2020
The term phenotype can be applied to any property observable in an organism or in specimens obtained from an organism. By genetic analysis phenotypes can be attributed to the action of certain genes whose presence in an individual organism is inferred from the phenotype and the pedigree. The complement of genes present in an organism is called the genotype. In diploid organisms such as humans there are two complete sets of the genes carried on the autosomes, those chromosomes other than the X and Y. A pair of genes occupies a specific place in the genome called a locus. Commonly the term genotype is used in reference to only the two genes at the one locus relevant to a specific phenotype. Alternative forms of a gene which can occupy the same locus are called alleles. An individual who has two different genes at one locus is said to be heterozygous at that locus, or a heterozygote. An individual who has two copies of the same gene at one locus is said to be homozygous at that locus, or a homozygote.
Whole genome sequencing and inheritance-based variant filtering as a tool for unraveling missing heritability in pediatric cancer
Published in Pediatric Hematology and Oncology, 2023
Charlotte Derpoorter, Ruben Van Paemel, Katrien Vandemeulebroecke, Jolien Vanhooren, Bram De Wilde, Geneviève Laureys, Tim Lammens
Identification of candidate variants was performed using an inheritance-based filtering approach. This strategy filters variants according to genotype requirements that meet an autosomal dominant, recessive or compound heterozygous inheritance pattern in this family. More specifically, in an autosomal dominant model, patients and obligate carriers must be heterozygous and unrelated spouses must be homozygous reference. In a recessive model, both patients must be homozygous alternative and their parents should be heterozygous. Other family members cannot be homozygous alternative. In a compound heterozygous inheritance, the phenotype is caused by two heterozygous recessive alleles at different loci in a particular gene and variants were filtered accordingly. In addition, exonic and non-exonic variants were compared respectively to the databases ExAC (non-Finnish European subset, ExAC-NFE)13 and 1000 Genomes (European subset, 1000G-EUR)14 for their absence or rarity in the general population (allele frequency (AF) ≤ 0.01).
Fat mass and obesity-associated (FTO) and leptin receptor (LEPR) gene polymorphisms in Egyptian obese subjects
Published in Archives of Physiology and Biochemistry, 2021
Ehab M. M. Ali, Thoria Diab, Afaf Elsaid, Hamada A. Abd El Daim, Rami M. Elshazli, Ahmad Settin
The data processing and analysis were done using the IBM Statistical Package of Social Science (SPSS, version 25.0, Thousand Oaks, CA). The continuous variables were analysed and compared as means ± standard deviation (M±SD) using Student’s t test, while the categorical variables were processed as numbers with percentage (n, %) using Fisher’s exact test with odds ratio (OR) and the 95% confidence interval (95% CI). The frequencies of the genotypes and alleles of FTO T>A (rs9939609) and LEPR Q223R (rs1137101) variants among obese subjects compared with healthy controls were calculated using Fisher’s exact test with two-tailed p values. The models designed for evaluating genetic inheritance of FTO T>A (rs9939609) and LEPR Q223R (rs1137101) variants include allelic, dominant, recessive, heterozygote, and homozygote. In the allelic model, the rare allele was emulated with the common allele in obese subjects and healthy control groups. In the dominant model, the rare allele carriage was compared vs. the common genotype, while in the recessive model, the rare genotype was compared vs. the other genotypes. Moreover, in the heterozygote and homozygote models, the heterozygote and homozygote genotypes were compared with the common genotype (Elsaid et al.2018). The equilibrium and disequilibrium between obese subjects vs. healthy controls were estimated using the Hardy–Weinberg equation. The p values achieved a statistically significant with a level below to .05.
Role of Glutathione-S-Transferases in Gallbladder Cancer and Cholelithiasis Susceptibility and Meta-Analysis
Published in Nutrition and Cancer, 2020
Manzoor Ahmad Malik, Subzar Ahmad Malik, Malik Gowharul Haq, Sadaf Ali Bangri, Sheikh Zahoor Ahmad, Omar Javed Shah, Zafar Amin Shah
Genotyping for GSTM1 and GSTT1 polymorphism was detected using the multiplex polymerase chain reaction (PCR) technique. Primers for GSTM1 and GSTT1 are shown in Table 1. The amplified products were identified by 2% electrophoresis in agarose gel and stained with ethidium bromide. The product lengths were 215, 480, and 312 bp for GSTM1, GSTT1 and CYP1A1, respectively (Fig. 1). The absence of PCR product for GSTM1 or GSTT1 in the presence of the CYP1A1 band was indicative of a null genotype for GSTM1 or GSTT1. Individuals with one or two copies of the relevant gene were classified as a “present” genotype and those with homozygous deletions as a “null” genotype. Ten percent of samples from both patients and controls were re-genotyped by other laboratory personnel and no discrepancy in genotyping was noticed.