MedGen Terms (T&T) Flashcards
The boundary between the 3’ end of an intron and the 5’ end of the following exon
Acceptor (or 3’) splice site
A type of chromosome with the centromere near one end
Acrocentric
Chromosomes 13, 14, 15, 21, 22
Acrocentric chromosomes
One of the alternative versions of a gene or DNA sequence at a given locus
Allele
An oligonucleotide probe synthesized to match a particular DNA sequence precisely and allow the discrimination of alleles that differ by only a single base
Allele-specific oligonucleotide (ASO)
The same or similar phenotypes are caused by different mutant alleles
Allelic heterogeneity
The ability of a test to perform correctly, measure what it is designed to measure
Analytic validity
Any chromosome number that is not an exact multiple of the haploid number
Aneuploidy
Birth defects resulting from malformations, deformations, or disruptions
Anomalies
The progressively earlier onset and increased severity of certain diseases in successive generations of a family
Anticipation
A three-base unit of RNA complementary to a codon in mRNA
Anticodon
Programmed cell death
Apoptosis
A group of abnormalities of unknown etiology and pathogenesis that is seen together more often than would be expected by chance
Association
Any nuclear chromosome other than the sex chromosomes
Autosome
A polymorphism maintained in the population by heterozygote advantage, allowing an allele, even if deleterious in the homozygous state, to persist at a relatively high frequency in the population
Balanced polymorphism
A technique which stains chromosomes in a characteristic pattern, allowing identification of individual chromosomes and structural abnormalities
Banding
The sex chromatin as seen in female somatic cells, representing an inactive X chromosome
Barr body
A pair of complementary nucleotide bases, used as the unit of measurement of the length of a DNA sequence
Base pair (bp)
A mathematical model used to calculate recurrence risk
Bayesian analysis
The ethical principle of behaving in a way that promotes the well-being of others
Beneficence
An abnormality present at birth, not necessarily genetic
Birth defect
Tumor-suppressor genes that are indirectly involved in controlling cellular proliferation by repairing DNA damage and maintaining genomic integrity, protecting from mutations that could lead to cancer
Caretaker genes
An individual heterozygous for a particular mutant allele; disease is not expressed
Carrier
The primary constriction on the chromosome, required for normal segregation in mitosis and meiosis
Centromere
The crossing of chromatid strands of homologous chromosomes, seen at the diplotene of the first meiotic dividion
Chiasma
An individual composed of cells derived from two genetically different zygotes; an inevitable result of transplantation
Chimera
The two parallel strands of chromatin, connected at the centromere, that constitute a chromosome after DNA synthesis
Chromatids
The complex of DNA and proteins of which chromosomes are composed
Chromatin
A small mass of chromatin containing genes for ribosomal RNA, at the end of the short arm of each chromatid of an acrocentric chromosome
Chromosomal satellite
One of the threadlike structures in the cell nucleus; consists of chromatin and carries genetic information
Chromosome
A clinical condition caused by an abnormal chromosome constitution in which there is duplication, loss, or rearrangement of chromosomal material
Chromosome disorder
A change in the genetic material at the chromosome level
Chromosome mutation
Refers to the relationship between two sequences that are on the same chromosome
Cis
The occurrence of clinically different phenotypes from mutations in the same gene
Clinical heterogeneity
The ability of a test to improve the medical care than an individual receives
Clinical utility
The ability of a test to detect the disease that the test was designed to detect
Clinical validity
Both alleles of a pair are expressed in the heterozygous state
Codominant
A triplet of three bases in a DNA or RNA molecule, specifying a single amino acid
Codon
The probability that an individual homozygous at a locus received both alleles from one ancestor
Coefficient of inbreeding (F)
A fluorescence hybridization technique used to compare two different DNA samples with respect to their relative content of a particular DNA segment or segments
Comparative genome hybridization (CGH)
A pattern of inheritance that is not mendelian, usually results from alleles at more than one locus interacting with environmental factors
Complex inheritance/Multifactorial inheritance
An individual, or genotype, with two different mutant alleles at the same locus
Compound heterozygote
Mosaicism present in the placenta but not present in the fetus
Confined placental mosaicism
Present at birth, not necessarily genetic
Congenital
Related by descent from a common ancestor
Consanguinity
A syndrome resulting from a microdeletion of chromosomal DNA extending over two or more loci
Contiguous gene syndrome
A variation in DNA sequence defined by the presence or absence of a segment of DNA, ranging from 200bp to 2Mb
Copy number variant (CNV)
If a DNA variant has an allele frequency >1%
Copy number polymorphism (CNP)
A procedure used in prenatal diagnosis to obtain a sample of fetal blood directly from the placenta
Cordocentesis
A procedure used in prenatal diagnosis to obtain amniotic fluid
Amniocentesis
A procedure used for prenatal diagnosis, where fetal tissue for analysis is withdrawn during 10-13wks gestation
Chorionic villus sampling (CVS)
A measure of correlation that varies from 1 for perfect positive to -1 for perfect negative
Correlation coefficient (r); 0 indicating there is no correlation
The reciprocal exchange of segments between chromatids of homologous chromosomes
Crossover
The study of chromosomes
Cytogenetics
The fetal cells of the chorionic villi that are sampled for karyotyping and DNA analysis
Cytotrophoblast
The two individual chromosomes formed when a single chromosome composed of paired chromatids separates at the centromere in anaphase of cell division
Daughter chromosomes
A recognizable pattern of dysmorphic features caused by extrinsic factors that affect the fetus in utero
Deformation syndrome
the distance between two individuals in a pedigree
Degree of relationship
The loss of sequence of DNA from a chromosome
Deletion
A structurally abnormal chromosome with two centromeres
Dicentric
The process whereby a cell acquires a tissue-specific pattern of expression of genes and proteins and a characteristic phenotype
Differentiation
The number of chromosomes in most somatic cells
Diploid
A birth defect caused by destruction of tissue; may be caused by vascular occlusion, a teratogen, or rupture of the amniotic sac with entrapment
Disruption
Twins produced by two separate ova, separately fertilized
Dizygotic twins
The molecule that encodes the genes responsible for the structure and function of living organisms and allows the transmission of genetic information
DNA
An enzyme that can synthesize a new DNA strand by using a previously synthesized DNA strand as a template
DNA polymerase
A trait phenotypically expressed in heterozygotes
Dominant
A disease-causing allele, or the effect of such an allele, that disrupts the function of a wild-type allele in the same cell
Dominant negative
As a consequence of X inactivation, the amount of product formed by the two copies of an X-linked gene in females is equivalent to the amount formed by the single gene in males
Dosage compensation
An individual who is heterozygous at each of two different loci
Double heterozygote (different from compound heterozygote!)
Expression of a gene at a time when it is not normally expressed
Dyschronic expression
Morphological developmental abnormalities, as seen in many syndromes of genetic or environmental origin
Dysmorphism
A disorder resulting from the interaction of a genetic predisposition to a specific disease with an environmental factor
Ecogenetic disorder
Expression of a gene in places where it is not normally expressed
Ectopic expression
A cell derived from the inner cell mass that is self-renewing in culture and can repopulate all the tissues of the embryo
Embryonic stem cell
The probability that a familial trait will occur in a family member based on observed numbers of affected and unaffected individuals
Empirical risk
A metabolic disorder resulting from deficiency or abnormality of a specific enzyme
Enzymopathy
Any factor that can affect gene function without change in the genotype
Epigenetic
Any chromosome number that is an exact multiple of the number of haploid gamete (n)
Euploid
A transcribed region of a gene that is present in mature messenger RNA
Exon
The extent to which a genetic defect is expressed
Expressivity
Any trait that is more common in relatives of an affected individual than in the general population, whether the cause is genetic, environmental, or both
Familial
Stage of intrauterine development from weeks 9 to 40
Fetal phase
FISH
flourescence in situ hybridization
The probability of transmitting one’s genes to the next generation compared with the average probability for the population
Fitness (f)
A high frequency of a mutant allele in a population founded by a small ancestral group when one or more of the founders was a carrier of the mutant allele
Founder effect
Nonstaining gap in the chromatin of a metaphase chromosome (ex:Xq27)
Fragile site; Xq27 is the fragile site for Fragile X syndrome
A mutation involving a deletion or insertion that is not an exact multiple of three base pairs, and thus changes the reading frame of the gene downstream of the mutation
Frameshift mutation
A mutation associated with an increase in one or more of the normal functions of a protein
Gain of function mutation
A reproductive cell with the haploid chromosome number
Gamete (ovum or sperm)
Tumor suppressor genes that directly regulate cell proliferation
Gatekeeper genes
A hereditary unit; a sequence of chromosomal DNA required for the production of a functional product
Gene
The number of copies of a particular gene in the genome
Gene dosage
A set of genes containing related exons, indicating that the genes have evolved from an ancestral gene by duplication and subsequent divergence
Gene family
Gradual diffusion of genes from one population to another across a barrier (may be physical or cultural, and may be breached by migration or mixing)
Gene flow
The characteristic arrangement of the genes on the chromosomes
Gene map
All the alleles present at a given locus or at all loci in the population
Gene pool
Treatment of a disease by introduction of DNA sequences that will have a therapeutic benefit
Gene therapy
Characteristic determined by genes
Genetic
The 64 triplets of bases that specify the 20 amino acids found in proteins
Genetic code
The ability of one mutant allele at a locus to correct for the loss of function associated with another allele at the same or another locus, demonstrating that the mutations are not identical
Genetic complementation
The provision of information and assistance to affected individuals or family members at risk of a disorder that may be genetic, concerning the consequences of the disorder, the probability of developing or transmitting it, and the ways in which it may be prevented
Genetic counseling (according to T&T)
A defect wholly or partly caused by a gene abnormality
Genetic disorder
Random fluctuation of allele frequencies in small populations
Genetic drift
The production of the same or similar phenotypes by different genetic mechanisms
Genetic heterogeneity
A mutant allele or genetically determined trait that leads to failure to reproduce, though not necessarily to death prior to reproduction
Genetic lethal
The sum total of death and disease caused by mutant genes
Genetic load
Testing on a population basis to identify individuals at risk of developing or of transmitting a specific disorder
Genetic screening
A genotype that determines a phenotype closely similar to that determined by a different genotype
Genocopy
The complete DNA sequence, containing the entire genetic information, or a gamete, an individual, a population, or a species
Genome
The chromosomal DNA sequence of a gene or segment of a gene, including the DNA sequence of noncoding and coding regions
Genomic DNA
The field of genetics concerned with structural and functional studies of the genome
Genomics
The alleles present at one locus, the genetic constitution of an individual as distinguished from the phenotype
Genotype
The cell line from which gametes are derived
Germline
The presence of two or more genetically different types of germline cells, resulting from mutation during the proliferation and differentiation of the germline
Germline mosaicism
The chromosome number of a normal gamete, with only one member of each chromosome pair
Haploid
A cause of genetic disease in which the contribution form a normal allele is insufficient to prevent disease because of a loss of function mutation at the other allele
Haploinsufficiency
A group of alleles in coupling at closely linked loci, usually inherited as a unit
Haplotype
The law that relates allele frequency to gentoype frequency, used in population genetics to determine allele frequency and heterozygote frequency when the incidence of a disorder is known
Hardy-Weinberg law (p^2 + 2pq + q^2)
The genotype of an individual with only one representative of a chromosome or chromosome segment, rather than the usual two; refers especially to X-linked genes in the male
Hemizygous
The fraction of total phenotypic variance of a quantitative trait that is due to genotypic differences
Heritability (h^2)
The presence of more than one type of mitochondrial DNA in the mitochondria of a single individual
Heteroplasmy
Any chromosome number other than the normal
Heteroploid
An individual or genotype with two different alleles at a given locus on a pair of homologous chromosomes
Heterozygote
A pair of chromosomes, one inherited paternally, the other maternally, that pair with each other during meiosis I, undergo crossover, and separate at anaphase I of meiosis
Homologous chromosomes
Genes in a single species, or in different species, that have overall similar DNA sequences, that may have related biochemical functions, and that arose from a common ancestral gene
Homologous genes
The presence of only one type of mitochondrial DNA in the mitochondria of a single individual
Homoplasmy
An individual or genotype with identical alleles at a given locus on a pair of homologous chromosome
Homozygote
Genes expressed in most or all cells because their products provide basic functions
Housekeeping genes
Proteins expressed in virtually every cell that have fundamental roles in the maintenance of cell structure and function
Housekeeping proteins
A major research project that took place from 1990-2003 and resulted in the sequencing of a representative human genome and the genomes of many model organisms
Human Genome Project
An abnormality of the placenta in which it grows to resemble a hydatid cyst, associated with very abnormal fetal development
Hydatidiform mole
Complete mole (karyotype and parental contribution)
46,XX karyotype, duplication of the chromosomes of the sperm with no maternal contribution
Partial mole (karyotype and parental contribution)
Triploid, usually with an extra paternal chromosome set
Two individuals in a family who have the same allele or alleles at a locus because they inherited the alleles from a common ancestor
Identity by descent
The phenomenon of different expression of alleles depending on the parent of origin
Imprinting (ex: Angelman syndrome, Prader-Willi syndrome)
A genetically determined biochemical disorder in which a specific protein defect produces a metabolic block that may have pathological consequences
Inborn error of metabolism
The mating of closely related individuals
Inbreeding
A trait that is inherited in a dominant manner, but is more severe in a homozygote than in a heterozygote
Incompletely dominant
The family member affected with a genetic disorder who is the first to draw attention to a pedigree
Index case or Proband
A deletion that does not destroy the normal reading frame of the gene
In-frame deletion
A chromosomal abnormality in which a DNA segment from one chromosome is inserted into another chromosome
Insertion
The ability of cells from patients with similar phenotypes, due to mutations in different genes, to correct one another
Intergenic complementation
A segment of a gene that is initially transcribed but then removed from within the primary RNA transcript by splicing together the sequences on either side of it
Intron
A chromosomal rearrangement in which a segment of a chromosome is reversed end to end
Inversion
Pericentric Inversion
Centromere is included in the inversion
Paracentric Inversion
Centromere is not included in the inversion
A reproductive technology in which sperm are allowed to fertilize an egg in tissue culture and the fertilized eggs are then introduced back into the uterus to allow implantation
In vitro fertilization
An abnormal chromosome in which one arm is duplicated
Isochromosome
The chromosome constitution of an individual; or the photomicrograph of the chromosomes of an individual systematically arranged
Karyotype
A unit of 1000 bases in a DNA or RNA sequence
kilobase (kb)
A statistical method in which the genotypes and phenotypes of parents and offspring in families are studied to determine whether two or more loci are assorting independently or exhibiting linkage during meiosis
Linkage analysis
Genes on the same chromosome which are transmitted together in meiosis more frequently than chance would allow
Linkage
The occurrence of specific combination of alleles in coupling phase at two or more linked loci more frequently than expected by chance from the frequency of the alleles in the population; proof is determined by a LOD score of 3 (1000:1 odds)
Linkage disequilibrium
The position occupied by a gene on a chromosome
Locus
The production of identical phenotypes by mutations at two or more different loci
Locus heterogeneity
A mutation associated with a reduction or a complete loss of one or more of th enormal functions of a protein
Loss-of-function mutation
Loss of a normal allele from a region of one chromosome of a pair, allowing a defective allele on the homologous chromosome to be clinically manifest
Loss of heterozygosity (LOH)
Original term used for the phenomenon of X-inactivation
Lyonization
The complex locus on chromosome 6p that includes the highly polymorphic human leukocyte antigen (HLA) genes
Major histocompatibility complex (MHC)
Behavior that harms others
Maleficence
A pattern of inheritance of a trait from a father to all of his sons and none of his daughters
Male-to-male transmission, or Holandric inheritance
A recognizable pattern of dysmorphic features having a single cause, either genetic or environmental
Malformation syndrome
A female heterozygous for an X-linked disorder in whom the trait is expressed clinically, typically due to nonrandom X inactivation
Manifesting heterozygote
The transmission of genetic information only through the mother
Maternal inheritance
Laboratory test that relies on measurement of the levels of particular substances, such as AFP, hCG, and uE3 in a pregnant woman’s blood, to screen for fetuses affected with certain trisomies or with neural tube defects
Maternal serum screening
A unit of 1,000,000 bases or base pairs in genomic DNA
megabase (Mb)
The type of cell division occurring in the germ cells, by which gametes containing the haploid chromosome number are produced from diploid cells
Meiosis
When does reduction in chromosome number take place>
Meiosis I
Patterns of inheritance that follow the classic laws of Mendel: autosomal dominant and recessive, and X-linked
Mendelian
A type of chromosome with a central centromere and arms of apparently equal length
Metacentric
Spread of malignant cells to other sites in the body
Metastasis
A chromosomal deletion that is too small to be seen under the microscope
Microdeletion
A mutation that changes a codon specific for one amino acid to specify another amino acid
Missense mutation
A step in oogenesis in which only a small sample of the total number of mitochondria is passed on to daughter cells, allowing significant variation in the proportions of mutant and wild-type mitochondria inherited by the daughter cells
Mitochondrial bottleneck
DNA with is only maternally inherited
Mitochondrial DNA
The inheritance of a trait encoded in the mitochondrial genome
Mitochondrial inheritance
The process of ordinary cell division, resulting in the formation of two cells genetically identical to the parent cell
Mitosis
A gene that alters the phenotype associated with mutations in a nonallelic gene
Modifier gene
A chromosome constitution in which one member of a chromosome pair is missing
Monosomy
Twins derived from a single zygote and thus genetically identical
Monozygotic twins
An individual or tissue with at least two cell lines differing in genotype or karyotype, derived from a single zygote
Mosaic
A pedigree in which there is more than one case of a particular disorder
Multiplex
A laboratory method that allows many different tests to be performed simultaneously on the same sample
Multiplex testing
An agent that increases the spontaneous mutation rate by causing changes in DNA
Mutagen
Any permanent heritable change in the sequence of genomic DNA
Mutation
The frequency of mutation at a given locus, expressed as mutation per locus per gamete (or per generation)
Mutation rate (mu)
The extent to which testing negative indicates that one does not have or will not develop the disease
Negative predictive value
An abnormal growth produced by imbalance between normal cellular proliferation and normal cellular attrition; may be benign or malignant
Neoplasia
The failure of tow members of a chromosome pair to disjoin during meiosis II or mitosis, so that both pass to one daughter cell and the other daughter cell receives neither
Nondisjunction
A single-base substitution in DNA resulting in a chain-termination (or stop) codon, preventing further synthesis of the polypeptide chain
Nonsense mutation
A technique used for detection of RNA molecules by hybridization to a complementary DNA probe
Northern blotting
An US finding of an echo-free space between the skin line and the soft tissue overlying the cervical spine in the subcutaneous tissue of the fetal neck; if increase, may be associated with fetal aneuploidy
Nuchal translucency
An allele that results in either the total absence of the gene product or in the total loss of function of the product
Null allele
An individual who may be clinically unaffected but on the basis of pedigree analysis must carry a specific mutant allele
Obligate heterozygote or carrier
A dominantly acting gene responsible for tumor development
Oncogene
The developmental history of an organism
Ontogeny
The short arm of a chromosome
p-arm
A phenomenon seen with the inheritance of unstable repeat expansion mutations in which expansion of the repeat occur preferentially when the mutation is transmitted by one parent versus the other
Parental transmission bias
A family history of a hereditary condition, or a diagram of a family history
Pedigree
The fraction of individuals with a genotype known to cause a disease who have nay signs or symptoms of the disease
Penetrance
The effects of a drug or its metabolites on physiological function and metabolic pathways
Pharmacodynamics
The area of biochemical genetics concerned with the impact of genetic variation on drub response and metabolism
Pharmacogenetics
The application of genomic information or methods to pharmocogenetic problems
Pharmacogenomics
The rate at which the body absorbs, transports, metabolizes, or excretes a drub or its metabolites
Pharmacokinetics
A mimic of a phenotype that is usually determined by a specific genotype, produced instead by the interaction of some environmental factor with a normal genotype
Phenocopy
The observed biochemical, physiological, and morphological characteristics of an individual, as determined by his or her genotype and the environment in which it is expressed; the abnormalities resulting from a particular mutant gene
Phenotype
The structurally abnormal chromosome 22 that typically occurs in a proportion of the bone marrow cells in most patients with CML; a reciprocal translocation between the distal portion of 22q and the distal portion of 9q
Philadelphia chromosome (Ph)
Multiple phenotypic effects of a single allele or pair of alleles; effects may not be obviously related
Pleiotropy
An embryonic cell that is capable of giving rise to different types of differentiated tissues or structures, depending on its location and environmental influences
Pluripotent
A single nucleotide base pair change in DNA
Point mutation
Inheritance determined by many genes at different loci, with small additive effects
Polygenic
The molecular genetic technique by which a short DNA or RNA sequence is amplified enormously by means of two flanking oligonucleotide primers used in repeated cycles of primer extension and DNA synthesis with DNA polymerase
Polymerase chain reaction (PCR)
The occurrence together in a population of two or more alternative genotypes, each at a frequency greater than which could be maintained by recurrent mutation alone
Polymorphism
Any multiple of the basic haploid chromosome number other than the diploid number (3n, 4n, etc)
Polyploid
The extent to which testing positive indicates that one has or will develop the disease
Positive predictive value
A type of prenatal diagnosis in which a cell is removed from a multi-cell embryo generated by IVF and tested for the presence of a disease-causing mutation
Preimplantation diagnosis (PGD)
In unstable repeat disorders, a moderate expansion of the number of repeats that is at increased risk of undergoing further expansion during meiosis and causing the full disorder in the offspring; can be asymptomatic
Premutation
A normal gene involved in some aspect of cell division or proliferation that may become activated by mutation or other mechanism to become an oncogene
Proto-oncogene
Segment of the X and Y chromosome, located at the most distal portion of their respective p and q arms, at which crossing over occurs during male meiosis; traits will appear to be inherited as autosomal traits
Pseudoautosomal region
A clinically benign allele that has a reduction in functional activity detected by in vitro assays but that has sufficient activity in vivo to prevent haploinsufficiency
Pseudodeficiency allele
An inactive gene within a gene family, derived by mutation of an ancestral active gene and frequently located within the same region of the chromosome as its functional counterpart
Pseudogene
The occurrence of a single cytogenetically abnormal cell in a cytogenetic analysis of a CVS or amnio specimen; generally considered artifactual and of no clinical significance
Pseudomosaicism
The long arm of a chromsome
q arm
The frequency of the less common allele of a pair
q (from Hardy-Weinberg)
The frequency of the more common allele of a pair
p (from Hardy-Weinberg)
A trait than an individual either has or does not have
Qualitative trait
A measurable quantity that differs among different individuals, often following a normal distribution in the population
Quantitative trait
Selection of a mate without regard to the genotype of the mate
Random mating
Chromosome breakage followed by reconstitution in an abnormal combination, can be balanced or unbalanced
Rearrangement
A trait that is expressed only in homozygotes, compound heterozygotes, or hemizygotes
Recessive
An individual who has a new combination of alleles not found in either parent
Recombinant
A chromosome that results from exchange of reciprocal segments by crossing over between a homologous pair of parental chromosomes during meiosis
Recombinant Chromosome
The formation of new combinations of alleles in coupling by crossing over between their loci
Recombination
The probability that a genetic disorder present in one or more members of a family will recur in another member of the same or a subsequent generation
Recurrence risk
A gene that codes for an RNA or protein molecule that regulates the expression of other genes
Regulatory gene
A comparison of the risk for a disease or trait in individuals who share a particular factor (such as genotype, environmental exposure, or a drug) versus the risk among individuals who lack the factor.
Relative risk
Random distribution of mitochondria into daughter cells
Replicative segregation
An enzyme, derived from bacteria, that can recognize a specific sequence of DNA and cleave the DNA molecule within the recognition site or at some nearby site
Restriction enzyme (endonuclease)
A polymorphic difference in DNA sequence between individuals that can be recognized by restriction enzymes
RFPL (restriction fragment length polymorphism)
A short sequence in DNA that can be recognized and cut by a specific restriction enzyme
Restriction site
A structurally abnormal chromosome in which the telomere of each chromosome arm has been deleted and the broken arms have reunited in ring formation
Ring chromosome
The probability of an event’s occurring, varying from 0 to 1
Risk
A nucleic acid formed on a DNA template, containing ribose instead of deoxyribose
RNA
An enzyme that synthesizes RNA on a DNA template
RNA polymerase
A translocation between two acrocentric chromosomes by fusion at or near the centromere, with loss of the short arms
Robertsonian translocation
The method widely used to determine the nucleotide sequence of a DNA molecule (not WES).
Sanger sequencing
DNA containing many tandem repeats of a short basic repeating unit
Satellite DNA (not the same as chromosomal satellite)
Loss of a small segment from one chromosome of a pair, resulting in hemizygosity for genes in that segment on the homologous chromosome
Segmental aneusomy
The disjunction of homologous chromosomes at meiosis
Segregation
A statistical method that assesses the phenotypes of individuals in families to determine the most likely mode of inheritance of a disease or trait
Segregation analysis
The frequency with which the test result is positive when the disorder is present
Sensitivity (TP/(TP+FP))
A recognizable pattern of dysmorphic features due to a number of different causes
Sequence
A trait that is not X-linked in its pattern of inheritance, but is expressed differently, either in degree or in frequency, in males and in females
Sex-influenced trait
A trait that is expressed in only one sex, although the gene that determines the trait is not X-linked
Sex-limited trait
A DNA sequence that acts in cis to decrease transcription of a nearby gene
Silencer
A mutant gene that has no detectable phenotypic effect
Silent allele
A disorder due to one or a pair of mutant alleles at a single locus
Single-gene disorder
A polymorphism in DNA sequence consisting of variation in a single base
(SNP) Single nucleotide polymorphism
A mutation occurring in a somatic cell rather than in the germline
Somatic mutation
A technique for preparation of a filter to which DNA has been transferred, following restriction enzyme digestion and gel electrophoresis to separate the DNA molecules by size
Southern blotting
The frequency with which a test result is negative when the disease is absent
Specificity (TN/(TN+FN))
A disease that is not the result of inheritance of a disease-causing allele from a parent, often the result of a new germline or somatic mutation
Sporadic
A type of cell capable both of self-renewal and of proliferation and differentiation
Stem cell
A gene coding for any RNA or protein product
Structural gene
A protein that serves a structural role in the body, such as collagen
Structural protein
A type of chromosome with arms of different lengths
Submetacentric
A characteristic pattern of anomalies, presumed to be causally related
Syndrome
A birth defect of the hands and feet characterized by extra digits and the fusion of adjoining digits
Synpolydactyly
The physical presence together on the same chromosome of two or more gene loci, whether or not they are close enough together for linkage to be demonstrated
Synteny
Two or more copies of the same or similar DNA sequence arranged in a direct succession along a chromosome
Tandem repeats
A cell with three copies of each chromosome, or an individual made up of such cells
Triploid
The state of having three representatives of a given chromosome instead of the usual pair
Trisomy
A normal gene involved in the regulation of cell proliferation, in which recessive mutations can lead to tumor development
Tumor-suppressor gene
The hypothesis that some forms of cancer can be initiated when both alleles of a tumor-suppressor gene become inactivated in the same cell
Two-hit hypothesis/model
A technique in which high frequency sound waves are used to examine internal body structures, useful in prenatal diagnosis
Ultrasonography
The presence in the karyotype of two copies of a specific chromosome, both inherited from one parent, with no representative of that chromosome from the other parent
Uniparental disomy
In UPD, if both homologues of the parental pair are present
Heterodisomy
In UPD, if one parental homologue is present in duplicate
Isodisomy
Diseases that occur when a gene contains tandemly repeating units of a few nucleotides and the number of such units increases beyond a threshold and interferes with the expression or function of that gene.
Unstable repeat expansion disorders
A technique used for the detection of proteins, usually by immunological methods
Western blotting
A term used to indicate the normal allele, or the normal phenotype
Wild-type
Reciprocal translocation between an X chromosome and an autosome
X;autosome translocation
Inactivation of genes on one X chromosome in comatic cells of female mammals, occurring early in embryonic life
X inactivation
The distinctive inheritance pattern of alleles at loci on the X chromosome that do not undergo recombination during male meiosis
X linkage
Genes on the Y chromsome, or traits determined by such genes, are Y linked
Y linkage
The number of zygotes from which a multiple birth is derived
Zygosity
A fertilized ovum
Zygote
One of three codons (UAG, UAA, and UGA) that terminate synthesis of a polypeptide
Stop codon (termination codon)
