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Gain-of-function mutation (GOF):

A DNA alteration which results in a new or enhanced protein activity.


The egg or sperm which contains a haploid set of 23 chromosomes.


See genetic counselor


See genomic DNA


A hereditary unit at a given chromosomal location consisting of a sequence of nucleotides (DNA) which encode a specific protein or RNA molecule.

Gene symbol:

The abbreviation of a gene name assigned by the HUGO Gene Nomenclature Committee. Human gene symbols consist of italicized uppercase letters and numbers (i.e. BRCA1).

Genetic code:

A sequence of three nucleotides (codons) which specify 20 amino acids that comprise proteins. DNA sequence can be used to predict mRNA sequence which determines the amino acid sequence of proteins. (COULD ADD CODON Table)

Genetic condition:

A disorder (disease) caused or influenced by genes that may or may not be passed on from parent to child.

Genetic counseling:

The process of providing patients and their families information regarding genetic-related disorders that can be used to make informed decisions. Education includes information regarding the disorder and its consequences, the probability of developing or transmitting a disorder (risk assessment), and ways to prevent or ameliorate a disorder.

Genetic counselor (GC):

A person who provides patients and their families education regarding genetic-related conditions and advocacy and support. Genetic counselors are health care professionals with graduate training in medical genetics and counseling that typically work as part of a healthcare team to provide patient education and support.

Genetic heterogeneity:

A similar phenotype caused by alterations of different genes or by a different genetic mechanism. Also known as heterogeneity. Compare to allelic heterogeneity, clinical heterogeneity, and locus heterogeneity.

Genetic predisposition:

A gene alteration which increases an individual’s susceptibility to develop a disease. The individual may or may not develop disease.


The study of heredity and inheritance patterns of traits or predispositions.

Genetic screening:

Testing a group of people to identify those at risk of developing or passing on a specific genetic disorder. An example is newborn screening for phenylketonuria (PKU).

Genetic testing:

Analysis of chromosomes or genetic markers in an individual’s genetic material from blood or other body tissue to diagnose or determine a predisposition for a genetic disease.

Genetic variant:

Any alteration of genetic material ranging from an entire chromosome to a single nucleotide. If the frequency or function of the alteration is unknown it is called a variant instead of a polymorphism or mutation.


All of the genetic information contained in the chromosomes of a gamete, individual, population or species.


A set of genomes that confer a specific genetic risk for a given disease.

Genomic DNA (gDNA):

Chromosomal DNA sequence inherited from germ cells and includes coding and non-coding regions. Contrast with mitochondrial DNA.


The study of gene structure and function.


Overall, the genetic constitution of an individual. Specifically, the inherited alleles at a given gene locus.

Genotype-phenotype correlation:

The association of a DNA variant (genotype) with a particular disease or trait (phenotype).

Germ cell:

A cell that becomes a sperm or egg.


The cell line that develops into sperm or eggs.

Germline mutation:

A DNA sequence alteration in the egg or sperm which can be passed to subsequent generations.


See gain-of-function mutation