NCI Dictionary of Genetics Terms

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Welcome to the NCI Dictionary of Genetics Terms, which contains technical definitions for more than 150 terms related to genetics. These definitions were developed by the PDQ® Cancer Genetics Editorial Board to support the evidence-based, peer-reviewed PDQ cancer genetics information summaries.

11 results found for: L
late or variable onset
(layt … VAYR-ee-uh-bul …)
The state in which a genetic trait is expressed later in life or is expressed at no fixed time in a life history.
LD
Where alleles (DNA markers) occur together more often than can be accounted for by chance because of their physical proximity on a chromosome. Also called linkage disequilibrium.
linkage
(LING-kij)
The tendency for genes or segments of DNA closely positioned along a chromosome to segregate together at meiosis, and therefore be inherited together.
linkage analysis
(LING-kij uh-NA-lih-sis)
A gene-hunting technique that traces patterns of disease in high-risk families. It attempts to locate a disease-causing gene by identifying genetic markers of known chromosomal location that are co-inherited with the trait of interest.
linkage disequilibrium
(LING-kij dis-EE-kwih-LIH-bree-um)
Where alleles (DNA markers) occur together more often than can be accounted for by chance because of their physical proximity on a chromosome. Also called LD.
locus
(LOH-kus)
The physical site or location of a specific gene on a chromosome.
locus heterogeneity
(LOH-kus HEH-teh-roh-jeh-NEE-ih-tee)
The same phenotype is caused by mutations in genes at different chromosomal loci.
LOD score
(… skor)
A statistical estimate of whether two genetic loci are physically near enough to each other (or "linked") on a particular chromosome that they are likely to be inherited together. A LOD score of 3 or higher is generally understood to mean that two genes are located close to each other on the chromosome. In terms of significance, a LOD score of 3 means the odds are 1,000:1 that the two genes are linked and therefore inherited together. Also called logarithm of the odds score.
logarithm of the odds score
(LAW-guh-RIH-thum … skor)
A statistical estimate of whether two genetic loci are physically near enough to each other (or "linked") on a particular chromosome that they are likely to be inherited together. A logarithm of the odds score of 3 or higher is generally understood to mean that two genes are located close to each other on the chromosome. In terms of significance, a logarithm of the odds score of 3 means the odds are 1,000:1 that the two genes are linked and therefore inherited together. Also called LOD score.
LOH
If there is one normal and one abnormal allele at a particular locus, as might be seen in an inherited autosomal dominant cancer susceptibility disorder, loss of the normal allele produces a locus with no normal function. When the loss of heterozygosity involves the normal allele, it creates a cell that is more likely to show malignant growth if the altered gene is a tumor suppressor gene. Also called loss of heterozygosity.
loss of heterozygosity
(… HEH-teh-roh-zy-GAH-sih-tee)
If there is one normal and one abnormal allele at a particular locus, as might be seen in an inherited autosomal dominant cancer susceptibility disorder, loss of the normal allele produces a locus with no normal function. When the loss of heterozygosity involves the normal allele, it creates a cell that is more likely to show malignant growth if the altered gene is a tumor suppressor gene. Also called LOH.