In genetics, the term synteny refers to two related concepts: In classical genetics, synteny describes the physical co-localization of genetic loci on the same chromosome within an individual or species. In current biology, synteny more commonly refers to colinearity, i.e. conservation of blocks of order within two sets of chromosomes that are being compared with each other. These blocks are referred to as syntenic blocks. The Encyclopædia Britannica gives the following description of synteny, using the modern definition: Etymology Synteny is a neologism meaning "on the same ribbon"; Greek: , syn "along with" + , tainiā "band". This can be interpreted classically as "on the same chromosome", or in the modern sense of having the same order of genes on two (homologous) strings of DNA (or chromosomes). : co-localization on a chromosome The classical concept is related to genetic linkage: Linkage between two loci is established by the observation of lower-than-expected recombination frequencies between them. In contrast, any loci on the same chromosome are by definition syntenic, even if their recombination frequency cannot be distinguished from unlinked loci by practical experiments. Thus, in theory, all linked loci are syntenic, but not all syntenic loci are necessarily linked. Similarly, in genomics, the genetic loci on a chromosome are syntenic regardless of whether this relationship can be established by experimental methods such as DNA sequencing/assembly, genome walking, physical localization or hap-mapping. Students of (classical) genetics employ the term synteny to describe the situation in which two genetic loci have been assigned to the same chromosome but still may be separated by a large enough distance in map units that genetic linkage has not been demonstrated. Across evolution: Shared synteny (also known as conserved synteny) describes preserved co-localization of genes on chromosomes of different species. During evolution, rearrangements to the genome such as chromosome translocations may separate two loci, resulting in the loss of synteny between them. Conversely, translocations can also join two previously separate pieces of chromosomes together, resulting in a gain of synteny between loci. Stronger-than-expected shared synteny can reflect selection for functional relationships between syntenic genes, such as combinations of alleles that are advantageous when inherited together, or shared regulatory mechanisms. In light of the more recent shift in the meaning of synteny, this conservation of gene content and linkage without preservation of order has also been termed mesosynteny. Current concept: gene-order preservation The term is currently (since ~2000) more