Genetic Principles
Gail S. Anderson in Biological Influences on Criminal Behavior, 2019
Every gene has a location, or a locus (plural loci), where it is found on the chromosome, almost like an address. For example, the gene for eye color may be on chromosome 3. (This is not a good example because eye color is actually governed by at least 20 genes and possibly by hundreds on several chromosomes,1 but let us pretend, for the sake of argument, that there is only one gene involved in eye color.) Let us say that the gene for eye color is 20 genes up on chromosome 3. You will always find the gene for eye color there; that is its address or locus. The sequence of genes on each chromosome is the same in both members of the pair. This is what the human genome project is all about—mapping the addresses for all the human genes. So, in our artificial example, the gene for eye color resides on chromosome 3, but this gene can have several different forms. It can be blue or gray or brown or green or violet or hazel. Each of these different versions of the gene is called an allele. So, an allele is a gene, but it is a more specific term. A gene that has more than one allele is termed polymorphic. In this example, the gene is for eye color; the alleles would be a blue allele, a green allele, and so on. Some genes have only one allele, in which case the words gene and allele are interchangeable. Some may have two or more. The proportion of each allele in the population, however, is not equal, in that one allele may be much more common than other alleles. For example, 70% of the alleles for one trait might be A, 20% B, 8% D, and only 2% E.
Genomics and Hearing Loss: Toward a New Standard of Care?
Stavros Hatzopoulos, Andrea Ciorba, Mark Krumm in Advances in Audiology and Hearing Science, 2020
The genotype of an individual is determined by alleles (variant form of a gene) that are received from the individual’s parents. The alleles contribute to the organism’s phenotype, which is the combination of an individual’s observable characteristics or traits, such as its morphology, development, physiological properties, and behavior. The phenotype is the result of the expression of an individual’s genotype, but also of the influence of environmental factors and the interactions between the two. The alleles of an individual control if a trait is dominant or recessive. Traits are dominant if only one copy of the allele is required for expression of the trait. Traits are recessive if two copies of an allele are required for expression of the trait. X-linked traits are those controlled by an allele that is carried on the X chromosome, while autosomal characteristics are controlled by alleles located on any “nonsexual” chromosome, that is, excluding the chromosomes X or Y. For any given phenotypical characteristic, an individual inherits one gene from each parent so that the individual has a pairing of two genes. If the two alleles that form the pair for a trait are identical, then the individual is said to be homozygous for that characteristic and if not, the individual is then heterozygous.
Cancer Biology and Genetics for Non-Biologists
Trevor F. Cox in Medical Statistics for Cancer Studies, 2022
A gene can have different codings, and these variants are called alleles. One allele is inherited from your mother and one from your father for each gene, and these determine your physical traits (phenotype), such as hair colour, height, etc. The combination of the alleles that you have inherited make up your genotype, but we can also use this term for a particular gene. If there are two possible alleles for a gene, A and a, there are three possible genotypes, AA, Aa and aa, depending on which alleles you inherited. For example, the OCA2 gene on chromosome 15 is associated with melanin production, which is a pigment for hair, eye and skin colour. A might be the allele for brown eyes and a for blue eyes. A is dominant and a is recessive, and so individuals with AA and Aa will have brown eyes, and individuals with aa will have blue eyes. But eye colour is not quite so simple as this as other genes are also involved. The allele that codes for the most common phenotype is called the wild type allele.
Evaluation of diallelic STR markers with inter-population allelic database for their usefulness in paternity trios in the Central Indian population
Published in Annals of Human Biology, 2021
Hirak Ranjan Dash, Kamayani Vajpayee, Radhika Agarwal, Anubha Gang, Ritesh Shukla, Ankit Srivastava
The genome of an offspring contains two alleles from each parent, assigned as obligate alleles. The finding of such alleles straightforwardly determines the father-child relationship when the mother is considered to be known in a case of paternity dispute (Grover et al. 2017). Two obligate alleles appear in instances when both the mother and child possess the consistent heterozygous genotype. Such occasions were observed rarely in an average of 16.08 instances in 100 paternity dispute cases tested in this study, where highest incidences were observed at D19S433 (32 occasions) and the lowest at SE33 (3 occasions). The number of instances of one or two obligate alleles was compared with forensic and paternity parameters (Dixit et al. 2019) for their possible correlation. A statistically significant positive correlation (p < 0.005) was observed between the occurrence of one obligate allele in STR markers with Power of Discrimination (PD), Polymorphic Information Content (PIC), Power of Exclusion (PE), Paternity Index (PI), and Observed and Expected Heterozygosity (Ho and He), whereas a statistically significant negative correlation (p < 0.005) was observed with Matching Probability (Pm) (Table 2). This strongly suggests the influence of the aforementioned forensic and paternity parameters on the observance of only one obligate allele in disputed paternity cases in the central Indian population.
Whole blood dynamic platelet aggregation counting and 1-year clinical outcomes in patients with coronary heart diseases treated with clopidogrel
Published in Platelets, 2021
Huaibin Wan, Weichao Han, Zhihao Wu, Zhenbang Lie, Daqiang Li, Shaohui Su
Genomic DNA was isolated from peripheral whole-blood specimens using the QIAamp Blood Kit (Qiagen, Hilden, Germany) according to the manufacturer’s instructions. Genotyping for known variants of CYP2C19*2, *3, and *17 were performed using a Pyro sequencing reaction general kit (3G Biotech, Changsha, China) and a detection system (QIAGEN PyroMark Q24 vacuum workstation, Germany). Base numbering and allele definitions follow the nomenclature of the Human Cytochrome P450 (CYP) Allele Nomenclature Committee (www.cypalleles.ki.se). The SNP genotypes were translated into star-allele genotypes. The combination of two alleles comprises a genotype. The patients were classified as extensive metabolizers, defined as two alleles conferring normal activity, near-normal activity, or individuals with an allele conferring decreased activity and a CYP2C19*17 (EMs: *1/*1, *1/*17, *17/*17, *2/*17, *3/*17). Reduced metabolizers defined by at least one reduced function allele except integrating with a CYP2C19*17 (RMs: *1/*2, *1/*3, *2/*2, *2/*3, *3/*3).
Important pharmacogenomic aspects in the management of HIV/AIDS
Published in South African Family Practice, 2019
A Marais, E Osuch, V Steenkamp, L Ledwaba
Approximately 80% of all drugs are metabolized by the hepatic cytochrome P450 enzyme system, of which the phase 1 metabolism iso-forms CYP1A2 (8.9%), CYP2C9 (12.8%), CYP2C19 (6.8%), CYP2D6 (20%), and CYP3A4/CYP3A5 (30.2%) are the most important.6 Each CYP450 enzyme is encoded for by a specific gene, which in turn is determined by inherited alleles – one from each parent. These alleles contribute to the phenotype (observable characteristics) of the individual, and may either be dominant or recessive.7 When heterozygous alleles are present, the dominant allele will determine the phenotype. Alleles occurring most commonly in the general population are known as “wild type” (or normal), whereas “variant” (or mutation) recessive alleles will only determine the phenotype if a homozygous combination is present. Sequence variations (or Single Nucleotide Polymorphisms/variations – SNPs or SNVs) may occur when a variant allele replaces one or both wild-type alleles. Every individual SNV is allocated a unique reference SNP ID number (rs#) by the HUGO Gene Nomenclature Committee (HGNC) – established by the US National Human Genome Research institute and the Wellcome Trust, to ensure unambiguous reference to genes in scientific communications.8 Variant alleles usually encode an enzyme or protein that has reduced (or no) activity, resulting in phenotypical changes which may have an altered effect on drug metabolism or response.9
Related Knowledge Centers
- DNA
- Multicellular Organism
- Nucleotide
- Phenotypic Trait
- Locus
- Single-Nucleotide Polymorphism
- Base Pair
- Pea
- Chromosome
- Biological Life Cycle