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 molecules present and operating in the cell. Expressed genes include those that are transcribed (copied) 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)
Genotype: The genetic makeup of an individual; usually refers to the DNA structure of a particular gene being analyzed.
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 that 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.