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NCI Dictionary of Genetics Terms


20 results found for: S



  • Sanger sequencing  listen  (SANG-er SEE-kwen-sing)
    A low-throughput method used to determine a portion of the nucleotide sequence of an individual’s genome. This technique uses polymerase chain reaction (PCR) amplification of genetic regions of interest followed by sequencing of PCR products.

  • screening  listen  (SKREE-ning)
    Clinical evaluation of an asymptomatic individual in the general population aimed at identifying abnormalities which might signal the presence of a specific medical condition. The intent is to find diseases at the earliest possible stage in their development in order to improve the chances for cure or reduce morbidity.

  • SDR 
    The aunts, uncles, grandparents, grandchildren, nieces, nephews, or half-siblings of an individual. Also called second-degree relative.

  • second-degree relative  listen  (SEH-kund-deh-GREE REH-luh-tiv)
    The aunts, uncles, grandparents, grandchildren, nieces, nephews, or half-siblings of an individual. Also called SDR.

  • segregation analysis  listen  (SEH-greh-GAY-shun uh-NA-lih-sis)
    The process of fitting formal genetic models to data on expressed disease characteristics (phenotype) in biological family members in order to determine the most likely mode of inheritance for the trait or disease under study.

  • sensitivity  listen  (SEN-sih-TIH-vih-tee)
    The frequency with which a test yields a true positive result among individuals who actually have the disease or the gene mutation in question. A test with high sensitivity has a low false-negative rate and thus does a good job of correctly identifying affected individuals.

  • simplex case  listen  (SIM-plex kays)
    A single, isolated occurrence of an inherited condition in a family. Simplex cases can result from certain inheritance patterns or be caused by de novo mutations or reduced penetrance within the family. It can also result from nongenetic causes such as adoption or alternate paternity.

  • single nucleotide polymorphism  listen  (SING-gul NOO-klee-oh-tide PAH-lee-MOR-fih-zum)
    DNA sequence variations that occur when a single nucleotide (adenine, thymine, cytosine, or guanine) in the genome sequence is altered; usually present in at least 1% of the population. Also called SNP.

  • single-stranded conformation polymorphism analysis  listen  (SIN-gul-STRAN-ded KON-for-MAY-shun PAH-lee-MOR-fih-zum uh-NA-lih-sis)
    A laboratory test used to separate single-stranded nucleic acids based on subtle differences in their DNA sequence, often a single base pair, which results in a different secondary structure and a measurable difference in mobiity through a gel. Also called SSCP analysis.

  • single-stranded conformational polymorphism  listen  (SIN-gul-STRAN-ded KON-for-MAY-shuh-nul PAH-lee-MOR-fih-zum)
    A type of mutation scanning; the identification of abnormally-migrating single-stranded DNA segments on gel electrophoresis. Also called SSCP.

  • SNP  listen  (snip)
    DNA sequence variations that occur when a single nucleotide (adenine, thymine, cytosine, or guanine) in the genome sequence is altered; usually present in at least 1% of the population. Also called single nucleotide polymorphism.

  • Southern blot  listen  (SUH-thern blot)
    Electrophoresis-based technique used in genetic testing to detect large deletions in DNA that can be missed by PCR-based genetic testing methods.

  • specificity  listen  (SPEH-sih-FIH-sih-tee)
    The frequency with which a test yields a true negative result among individuals who do not have the disease or the gene mutation in question. A test with high specificity has a low false-positive rate and thus does a good job of correctly classifying unaffected individuals.

  • splice-site mutation  (... myoo-TAY-shun)
    An alteration in the DNA sequence that occurs at the boundary of an exon and an intron (splice site). This change can disrupt RNA splicing resulting in the loss of exons or the inclusion of introns and an altered protein-coding sequence.

  • splicing  listen  (SPLY-sing)
    The process by which introns, the noncoding regions of genes, are excised out of the primary messenger RNA transcript, and the exons (i.e., coding regions) are joined together to generate mature messenger RNA. The latter serves as the template for synthesis of a specific protein.

  • sporadic cancer  listen  (spuh-RA-dik KAN-ser)
    This term has two meanings. It is sometimes used to differentiate cancers occurring in people who do not have a germline mutation that confers increased susceptibility to cancer from cancers occurring in people who are known to carry a mutation. Cancer developing in people who do not carry a high-risk mutation is referred to as sporadic cancer. The distinction is not absolute, because genetic background may influence the likelihood of cancer even in the absence of a specific predisposing mutation. Alternatively, sporadic is also sometimes used to describe cancer occurring in individuals without a family history of cancer.

  • SSCP 
    A type of mutation scanning; the identification of abnormally-migrating single-stranded DNA segments on gel electrophoresis. Also called single-stranded conformational polymorphism.

  • SSCP analysis  listen  (… uh-NA-lih-sis)
    A laboratory test used to separate single-stranded nucleic acids based on subtle differences in their DNA sequence, often a single base pair, which results in a different secondary structure and a measurable difference in mobiity through a gel. Also called single-stranded conformation polymorphism analysis.

  • surveillance  listen  (ser-VAY-lents)
    Periodic clinical evaluation of an individual who is at increased risk of developing a condition (compared with the general population) aimed at detecting new or recurrent disease. In public health, surveillance may also refer to the systematic collection of information regarding the incidence, prevalence, and mortality related to various medical conditions or health-related events.

  • susceptibility gene  listen  (suh-SEP-tih-BIH-lih-tee jeen)
    A germline mutation that increases an individual’s susceptibility or predisposition to a certain disease or disorder. When such a mutation is inherited, development of symptoms is more likely, but not certain. Also called predisposing mutation.


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