Synteny

Gene order in chromosomes is conserved over wide evolutionary distances.

For many organisms, protein-coding genes have been mapped on the chromosomes using a variety of techniques.

In many comparisons, large segments of chromosomes (or sometime entire chromosomes) were found to have the same order of genes. However, the spacing between mapped genes, even in molecular maps, was not always proportional. For example, the diagram illustrates the synteny between humans and cats of five genes on the X chromosome (rev).

The identification and enumeration of shared chromosomal segments on which about 500 genes have been mapped reveals variation in the minimum number of evolutionary rearrangements required to account for the patterns. The table shows the minimum rearrangements separating humans from other mammals (rev). Between the closely related plants, Arabidopsis thaliana and Brassica oleracea (cabbage), there are at least 19 rearrangements (ref).

Mammal No. of Rearrangements

Cat 13

Cow 27

Pig 28

Rat 88

Rearrangements of chromosome segments occurred rarely during evolution. Deciphering the order of rearrangements should assist in understanding evolutionary relationships.
In some evolutionary lineages, rearrangements occurred more frequently than in others.
Genome contraction or expansion events occur more frequently than rearrangements.
Synteny should be highly useful for biotechnological applications. Knowing a little about the linkage of a desirable trait in an economically important, but not well studied, organism, allows the investigator to examine syntenic segments of a more well studied organism to identify genes that are candidates for the trait.

Extensive synteny has also been demonstrated for chromosomes of monocotyledonous plants (ref).
Within genera, bacteria exhibit considerable synteny. However, in intergeneric comparisons gene order appears not to have been conserved for large segments.
Only seven rearrangements appear to separate humans from a hypothetical primate ancestor.
Contraction-expansion events may, in part, be due to transposable element rearrangements.

E-mail inquiries to U. Melcher------------Last Updated: 13 November, 2000