Allelic heterogeneity

Different mutations in the same gene that cause different phenotypic manifestations or severity of disease.

False-positive result

A test result that indicates an individual is affected and/or has a certain gene mutation when he or she is actually unaffected and/or does not have the mutation; i.e., a positive test result in a truly unaffected or mutation-negative individual. (NCI Thesaurus)

Unclassified variant

A variation in a genetic sequence whose association with disease risk is unknown. Also called variant of unknown significance, variant of uncertain significance, and VUS.

Copy number variant

Refers to the genetic trait involving the number of copies of a particular gene present in the genome of an individual. Genetic variants, including insertions, deletions, and duplications of segments of DNA, are also collectively referred to as copy number variants. Copy number variants account for a significant proportion of the genetic variation among individuals. Also called CNV.

CNV

Refers to the genetic trait involving the number of copies of a particular gene present in the genome of an individual. Genetic variants, including insertions, deletions, and duplications of segments of DNA, are also collectively referred to as copy number variants. CNVs account for a significant proportion of the genetic variation among individuals. Also called copy number variant.

Genetic marker

An identifiable segment of DNA (e.g., Single Nucleotide Polymorphism [SNP], Restriction Fragment Length Polymorphism [RFLP], Variable Number of Tandem Repeats [VNTR], microsatellite) with enough variation between individuals that its inheritance and co-inheritance with alleles of a given gene can be traced; used in linkage analysis. (NCI Thesaurus)

Penetrance

A characteristic of a genotype; it refers to the likelihood that a clinical condition will occur when a particular genotype is present. (NCI Thesaurus)

Dirty necrosis

Presence of necrotic cellular debris within the lumen of the neoplastic glands in the colorectal mucosa.

Band

When chromosomes at a particular stage in cell division are stained using one of several laboratory techniques, a specific pattern of light and dark stripes (bands) appears when the chromosomes are viewed through a microscope; the banding pattern assists in assigning each chromosome its particular number and evaluating its structure. (NCI Thesaurus)

Nucleotide

A molecule consisting of a nitrogen-containing base (adenine, guanine, thymine, or cytosine in DNA; adenine, guanine, uracil, or cytosine in RNA), a phosphate group, and a sugar (deoxyribose in DNA; ribose in RNA). DNA and RNA are polymers comprised of many nucleotides, strung together like beads in a necklace. (NCI Thesaurus)

Propositus

The male individual through whom a family with a genetic disorder is ascertained. In females this is called a proposita.

Proposita

The female individual through whom a family with a genetic disorder is ascertained. In males this is called a propositus.

Proband

The individual through whom a family with a genetic disorder is ascertained. In males this is called a propositus, and in females it is called a proposita. (NCI Thesaurus)

Haplotype

A set of closely linked genetic markers present on one chromosome which tend to be inherited together. (NCI Thesaurus)

Cosegregation

The transmission, together, of 2 or more genes on the same chromosome, as a result of their being in very close physical proximity to one another (i.e., linked).