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G

Gamete
Mature male or female reproductive cell (sperm or ovum) with a haploid set of chromosomes (23 for humans).

GC-rich area
Many DNA sequences carry long stretches of repeated G and C which often indicate a gene-rich region.

Gel electrophoresis
See: electrophoresis

Gene
The fundamental physical and functional unit of heredity. A gene is an ordered sequence of nucleotides located in a particular position on a particular chromosome that encodes a specific functional product (i.e., a protein or RNA molecule). Genes are pieces of DNA, and most genes contain the information for making a specific protein.
See also: gene expression

Gene amplification
Repeated copying of a piece of DNA; a characteristic of tumor cells.
See also: gene, oncogene

Gene chip technology
Development of cDNA microarrays from a large number of genes. Used to monitor and measure changes in gene expression for each gene represented on the chip.

Gene expression
The process by which a gene's coded information is converted into the structures present and operating in the cell. Expressed genes include those that are transcribed into mRNA and then translated into protein and those that are transcribed into RNA but not translated into protein (e.g., transfer and ribosomal RNAs).

Gene family
Group of closely related genes that make similar products.

Gene library
See: genomic library

Gene mapping
Determination of the relative positions of genes on a DNA molecule (chromosome or plasmid) and of the distance, in linkage units or physical units, between them.

Gene pool
All the variations of genes in a species.
See also: allele, gene, polymorphism

Gene prediction
Predictions of possible genes made by a computer program based on how well a stretch of DNA sequence matches known gene sequences

Gene product
The biochemical material, either RNA or protein, resulting from expression of a gene. The amount of gene product is used to measure how active a gene is; abnormal amounts can be correlated with disease-causing alleles.

Gene testing
See: genetic testing, genetic screening

Gene therapy
An experimental procedure aimed at replacing, manipulating, or supplementing nonfunctional or misfunctioning genes with healthy genes.
See also: gene, inherit, somatic cell gene therapy, germ line gene therapy

Gene transfer
Incorporation of new DNA into and organism's cells, usually by a vector such as a modified virus. Used in gene therapy.
See also: mutation, gene therapy, vector

Genetic code
The sequence of nucleotides, coded in triplets (codons) along the mRNA, that determines the sequence of amino acids in protein synthesis. A gene's DNA sequence can be used to predict the mRNA sequence, and the genetic code can in turn be used to predict the amino acid sequence. It is the instructions in a gene that tell the cell how to make a specific protein. A, T, G, and C are the "letters" of the DNA code; they stand for the chemicals adenine, thymine, guanine, and cytosine, respectively, that make up the nucleotide bases of DNA. Each gene's code combines the four chemicals in various ways to spell out 3-letter "words" that specify which amino acid is needed at every step in making a protein.

Genetic counseling
Provides patients and their families with education and information about genetic-related conditions and helps them make informed decisions.

Genetic discrimination
Prejudice against those who have or are likely to develop an inherited disorder.

Genetic engineering
Altering the genetic material of cells or organisms to enable them to make new substances or perform new functions.

Genetic engineering technology
See: recombinant DNA technology

Genetic illness
Sickness, physical disability, or other disorder resulting from the inheritance of one or more deleterious alleles.

Genetic informatics
See: bioinformatics

Genetic map
See: linkage map

Genetic marker
A gene or other identifiable portion of DNA whose inheritance can be followed.
See also: chromosome, DNA, gene, inherit

Genetic material
See: genome

Genetic mosaic
An organism in which different cells contain different genetic sequence. This can be the result of a mutation during development or fusion of embryos at an early developmental stage.

Genetic polymorphism
Difference in DNA sequence among individuals, groups, or populations (e.g., genes for blue eyes versus brown eyes).

Genetic predisposition
Susceptibility to a genetic disease. May or may not result in actual development of the disease.

Genetic screening
Testing a group of people to identify individuals at high risk of having or passing on a specific genetic disorder.

Genetic testing
Analyzing an individual's genetic material to determine predisposition to a particular health condition or to confirm a diagnosis of genetic disease.

Genetics
The study of inheritance patterns of specific traits.

Genome
All the genetic material in the chromosomes of a particular organism; its size is generally given as its total number of base pairs.

Genome project
Research and technology-development effort aimed at mapping and sequencing the genome of human beings and certain model organisms.
See also: Human Genome Initiative

Genomic library
A collection of clones made from a set of randomly generated overlapping DNA fragments that represent the entire genome of an organism.
See also: library, arrayed library

Genomic sequence
See: DNA

Genomics
The study of genes and their function.

Genotype
The genetic constitution of an organism, as distinguished from its physical appearance (its phenotype).

Germ cell
Sperm and egg cells and their precursors. Germ cells are haploid and have only one set of chromosomes (23 in all), while all other cells have two copies (46 in all).

Germ line
The continuation of a set of genetic information from one generation to the next.
See also: inherit

Germ line gene therapy
An experimental process of inserting genes into germ cells or fertilized eggs to cause a genetic change that can be passed on to offspring. May be used to alleviate effects associated with a genetic disease.
See also: genomics, somatic cell gene therapy.

Germ line genetic mutation
See: mutation

Guanine (G)
A nitrogenous base, one member of the base pair GC (guanine and cytosine) in DNA.
It is one of the four bases in DNA that make up the letters ATGC, guanine is the "G". The others are adenine, cytosine, and thymine. Guanine always pairs with cytosine.
See also: base pair, nucleotide

Gyandromorph
Organisms that have both male and female cells and therefore express both male and female characteristics.


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