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:

Genomic sequencing and mapping have enabled comparison of the general structures of genomes of many different species. The general finding is that organisms of relatively recent divergence show similar blocks of genes in the same relative positions in the genome. This situation is called synteny, translated roughly as possessing common chromosome sequences. For example, many of the genes of humans are syntenic with those of other mammals—not only apes but also cows, mice, and so on. Study of synteny can show how the genome is cut and pasted in the course of evolution.