Orthologous genes flanking each GRIN2 genes define a synteny with high degree of conservation among human, mouse, zebra finch and chicken. (A) The tetrapod GRIN2A paralogon has two fish paralogons, the GRIN2A-1 paralogon and the GRIN2A-2 paralogon. AXIN1 on human chromosome 16, zebra finch chromosome 14 and chicken chromosome 14 near GRIN2A have two co-orthologs located in medaka chromosomes 1 and 8. The tetrapod GRIN2B paralogon has two fish paralogons, the GRIN2B-1 paralogon and the GRIN2B-2 paralogon (B). PDE6H on human chromosome 12, mouse chromosome 6, zebra finch chromosome 1A and chicken chromosome 1 near GRIN2B have two co-orthologs located in medaka chromosomes 1 and 8. (C) The tetrapod GRIN2C paralogon has two fish paralogons, the GRIN2C-1 paralogon and the GRIN2C-2 paralogon. Each of the SOX9, AATK and CYTH1 on human chromosome 17 near GRIN2C has two co-orthologs in zebrafish chromosomes 3 and 12 and, also, two co-orthologs in tetraodon chromosomes 2 and 3. Each GRIN2D paralogons (D) define a synteny with high degree of conservation among the studied tetrapod and fish species. The positions of genes on chromosomes are not drawn to scale.