Glossary of Genetics Terms
ABCC6: ABCC6 belongs to the ATP-binding cassette (ABC) gene sub-family "C" which include genes such as MRP1 to 6 (ABCC1-6) and the Cystic Fibrosis Transmembrane conductance Regulator gene (ABCC7 or CFTR). ABCC6 encodes a protein of 1503 amino acids located in the plasma membrane with probably 17 membrane-spanning helices grouped into three transmembrane domains.
Autosome (autosomal): A chromosome not involved in sex determination. The diploid human genome consists of 46 chromosomes, 22 pairs of autosomes, and 1 pair of sex chromosomes (the X and Y chromosomes).
Autosomal dominant inheritance: A gene that almost always results in a specific physical characteristic, for example, a disease, even though the patient's genome possesses only one copy. With a dominant gene, the chance of passing on the gene (and therefore the disease) to children is 50-50 in each pregnancy.
Autosomal recessive inheritance: A genetic disorder that appears only in patients who have received two copies of a mutant gene, one from each parent.
Base pair (bp): Two nitrogenous bases (adenine and thymine or guanine and cytosine) held together by weak bonds. Two strands of DNA are held together in the shape of a double helix by the bonds between base pairs.
Base sequence: The order of nucleotide bases in a DNA molecule.
Base sequence analysis: A method, sometimes automated, for determining the base sequence.
Chromosomes: The self-replicating genetic structures of cells containing the cellular DNA that bears in its nucleotide sequence the linear array of genes. In prokaryotes, chromosomal DNA is circular, and the entire genome is carried on one chromosome. Eukaryotic genomes consist of a number of chromosomes whose DNA is associated with different kinds of proteins.
DNA (deoxyribonucleic acid): The molecule that encodes genetic information. DNA is a double- stranded molecule held together by weak bonds between base pairs of nucleotides. The four nucleotides in DNA contain the bases: adenine (A), guanine (G), cytosine (C), and thymine (T). In nature, base pairs form only between A and T and between G and C; thus the base sequence of each single strand can be deduced from that of its partner.
DNA sequence: The relative order of base pairs, whether in a fragment of DNA, a gene, a chromosome, or an entire genome. See base sequence analysis.
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). See gene expression.
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 families: Groups of closely related genes that make similar products.
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 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.
Genetic code: The sequence of nucleotides, coded in triplets (codons) along the mRNA, that determines the sequence of amino acids in protein synthesis. The DNA sequence of a gene can be used to predict the mRNA sequence, and the genetic code can in turn be used to predict the amino acid sequence.
Genetics: The study of the patterns of inheritance of specific traits.
Genome: All the DNA contained in an organism or a cell, which includes both the chromosomes within the nucleus and the DNA in mitochondria.
Mutation: A change in the arrangement of the parts of a gene to make an altered gene or protein product.
Pedigree: A simplified diagram of a family's genealogy that shows family members' relationships to each other and how a particular trait or disease has been inherited.
Phenotype: The observable traits or characteristics of an organism, for example hair color, weight, or the presence or absence of a disease. Phenotypic traits are not necessarily genetic.
Sequence: See base sequence.
Single-gene disorder: Hereditary disorder caused by a mutant allele of a single gene (e.g., Duchenne muscular dystrophy, retinoblastoma, sickle cell disease). Compare polygenic disorders.
Somatic cells: Any cell in the body except gametes and their precursors.