Hypermedia Glossary Of Genetic Terms
|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).
The degree of expression is called expressivity.
|Gene||The term coined by Johannsen (1909) for the fundamental physical and functional unit of heredity. The word gene was derived from De Vries' term pangen, itself a derivative of the word pangenesis which Darwin (1868) had coined. A gene is an ordered sequence of nucleotides located in a particular position (locus) on a particular chromosome that encodes a specific functional product (the gene product, i.e. a protein or RNA molecule). It includes regions involved in regulation of expression and regions that code for a specific functional product. See gene expression, allele.|
|Messenger RNA (mRNA)||RNA that serves as a template for protein synthesis or for synthesis of cDNA. See genetic code.|
|Protein||A large molecule composed of one or more chains of amino acids in a specific order; the order is determined by the base sequence of nucleotides in the gene coding for the protein. Proteins are required for the structure, function, and regulation of the bodys cells, tissues, and organs, and each protein has unique functions. Examples are hormones, enzymes, and antibodies.|
|Ribonucleic acid (RNA)||A chemical found in the nucleus and cytoplasm of cells; it plays an important role in protein synthesis and other chemical activities of the cell. The structure of RNA is similar to that of DNA. There are several classes of RNA molecules, including messenger RNA, transfer RNA, ribosomal RNA, and other small RNAs, each serving a different purpose.|
|Transfer RNA (tRNA)||A class of RNA having structures with triplet nucleotide sequences that are complementary sequences to the triplet nucleotide coding sequences of mRNA. The role of tRNAs in protein synthesis is to bond with amino acids and transfer them to the ribosomes, where proteins are assembled according to the genetic code carried by mRNA.|
|Ribosomal RNA (rRNA)||A class of RNA found in the ribosomes of cells.|
|Expressivity||Term coined by Voigt (1926) for the phenotypic expression of a gene or genotype, differs in type or degree from slight to intermediate to complete. It depends both on genotype and environment, and thus may be constant or variable between individuals or sexes. It is a qualitative measure.
C.f. Penetrance as a quantitative concept of gene expression.
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