Syntenie en evolutie

Synteny in classical terms refers to the genes present on the same chromosome, like beads on the same string.

For example, consider species X, which has genes A, B, and C present on one chromosome. These genes are said to be syntenic in species X.

Then consider another species, Y, with alleles A1, B1, and C1 on another chromosome. These genes are also said to be syntenic in species Y.

In evolutionary perspective, synteny refers to the phenomenon of co-localization of genes on a chromosome of two or more different species.

Therefore, the genes A and A1, B and B1 and C and C1 represent a synteny between the two species, X and Y.

In addition, the genes present in common chromosomal regions in two or more species, like the genes A, B and C, represent a conserved syntenic segment or conserved syntenic blocks.

During the course of evolution, species undergo random mutations, survive natural selection and evolve into several lineages all while mostly maintaining conserved syntenic blocks over many chromosomes.

For example, around 85 million years ago, humans and tree shrews shared a common mammalian ancestor. Even after millions of years of divergence, several genes present on the long arm of human chromosome 10 and the tree shrew’s chromosome 16 show conserved synteny in some regions.

This indicates that an ancestral mammalian chromosome evolved into chromosome 16 in the tree shrew, and also the long arm of chromosome 10 in humans.

Based on synteny analysis and high resolution DNA data from all known modern primates, scientists have proposed a karyotype for the common ancestor of all of these species.

The matching colors shown in the human and ancestral chromosomes indicate the conserved syntenic blocks and ancestral chromosomes from which human chromosomes evolved.

These ancestral chromosomes would have undergone several rounds of chromosome rearrangement, fusion or breakage, facilitating diversity and speciation into the primate species of today.