A glossary of relevant genetic terms. Deborah J. Morris-Rosendahl, PhD

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Bibliography. Morris-Rosendahl DJ. A glossary of relevant genetic terms. Dialogues Clin Neurosci. 2010;12(1):116-20. PubMed PMID: 20373673; PubMed Central PMCID: PMC3181945.
Ma. del Rocío Baños Lara
Flashcards by Ma. del Rocío Baños Lara, updated more than 1 year ago
Ma. del Rocío Baños Lara
Created by Ma. del Rocío Baños Lara almost 3 years ago
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Question Answer
Allele One of two or more alternate forms of a gene or marker at a particular locus on a chromosome.
Common disorder common variant (CDCV) hypothesis A theory that many common diseases are caused by common alleles that individually have little effect, but in concert confer a high risk.
Complex disease A disorder in which the cause is considered to be a combination of genetic effects and environmental influences.
Comparative genome hybridization (CGH) CGH is a molecular-cytogenetic method for the analy- sis of copy number changes (gains or losses) in the DNA content of a given individual’s DNA.
Compound heterozygosity Heterozygosity for two different mutant alleles of a gene, often the case for autosomal recessive disorders.
Copy number variation (CNV) A segment of DNA in which copy number differences have been found by comparison of two or more genomes. The segment may range from one kilobase to several megabases in size. The variation is usually due to deletion or duplication.
Deep resequencing A technique for sequencing a gene in several thousand subjects, typically using one of the new high-throughput sequencing technologies.
Epigenetics Heritable changes to DNA structure that do not alter the underlying DNA sequence, eg, DNA methylation.
Epigenomics The application of epigenetics to the whole genome.
Exome The approximately 1% of the human genome that com- prises all exons and therefore the entire protein-coding region of the genome.
Genetic association The nonrandom occurrence of a genetic marker (usu- ally a particular allele of a polymorphism) with a trait, which suggests an association between the genetic marker (or marker close to it) and disease pathogene- sis.
Genome In eukaryotes, the basic (monoploid) chromosome set, consisting of a species-specific number of linkage groups and the genes contained therein. For example, in humans, the genome consists of the 24 different chromosomes (22 autosomes, X and Y chromosomes). The mitochondrial DNA is usually considered to be a separate “mitochondrial” genome.
Genome-wide association study (GWAS) A test for the association between genetic polymorphisms spread evenly over the entire genome and a disease. Usually, at least 300 000 markers are required to adequately cover the genome.
Genotype The genetic constitution with respect to the alleles at one or more pairs of genetic loci under observation. The genotype of an individual is the sum total of the genetic information contained on the chromosomes, as distinguished from the individual’s phenotype (idiotype)
Haploid A single genome or set of chromosomes (eg, in human gametes, n=23), compared to the normal diploid (dou- ble) set of chromosomes (n=46).
Haplotype A combination of alleles at closely linked gene loci that are inherited together.
Hemizygous When one or more genes is present in only one, instead of two copies, eg, men are hemizygous for most genes on the X and Y chromosomes.
Heterozygous Having different alleles for one or more genes in homologous chromosome segments, as opposed to being homozygous with identical alleles at these loci.
Linkage Genetic linkage refers to the observation that two or more genes located on the same chromosome are inherited together. The ratio of being transmitted together versus being separated allows an estimate of their distance from each other (recombination fraction).
Methylation (of DNA) The attachment of a methyl group to DNA. In vertebrates, this typically occurs at CpG sites (cytosine-phosphate-guanine sites) in the DNA sequence, resulting in the conversion of cytosine to 5-methylcytosine
Monogenic disorder The disorder caused by one or more mutations in a single gene, eg, cystic fibrosis (mutations in the CFTR gene). Such disorders are also sometimes referred to Mendelian diseases.
Penetrance The frequency (in percent) with which a dominant or homozygous recessive gene or gene combination manifests itself in the phenotype of the carriers.
Pharmacogenetics A branch of genetics that deals with the genetic variability in individual responses to drugs and drug metabolism.
Phenocopy A nonhereditary, phenotypic modification (caused by special environmental conditions) that mimics a similar phenotype caused by a gene mutation.
Phenotype The observable properties (structural and functional) of an organism, produced by the interaction between the organism's genotype and the environment in which it finds itself.
Pleiotropy Genes or mutations that result in the production of multiple, apparently unrelated, effects at the phenotypic level. For example, patients with phenylketonuria, caused by mutations in the PAH (phenylalanine hydrox- ylase) gene, have reduced hair and skin pigmentation in addition to mental retardation, resulting from toxic levels of phenylalanine.
Polymorphism (genetic) A chromosome or DNA variant that is observed in natural populations. A gene locus is defined as polymorphic if a rare allele has a frequency of 0.01 (1%) or more.
Second- or next-generation sequencing (also referred to as high-throughput sequencing) New techniques that have increased the speed and decreased the cost of DNA sequencing by two orders of magnitude, enabling the sequencing of the entire genomes of many individuals.
Single nucleotide polymorphism (SNP) Heritable polymorphism resulting from a single base pair change. SNPs generally have only two alleles.
Structural variant Structural genomic variation includes any genetic variant that alters chromosomal structure, including inversions, translocations, duplications and deletions. Duplications and deletions, collectively known as CNVs (see copy number variation) are the most common form of structural variation in the human genome.
Synonymous nucleotide change/non-synonymous nucleotide change A change in the DNA sequence which does not result in the change in the amino acid sequence, eg, GTT>GTC both code for Valine (Val or V). A nonsynonymous change results in the coding of a different amino acid (eg, GTT>GAT results in Val>Asp).
Trinucleotide repeat expansion An increased number of contiguous trinucleotide repeats (eg, CAG, CGG) in the DNA sequence from one generation to the next. When the expansion extends into the pathological range, this type of mutation causes diseases such as Huntington’s disease, fragile X syn- drome, myotonic dystrophy, and many forms of spin- ocerebellar ataxia.
X-inactivation The random, early embryological, inactivation of one of the X chromosomes in females, so that the expression of X-chromosomal genes is the same as that in males.
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