ABSTRACT
Comparative genomics studies the evolutionary relationship between genes and the genomes of species from different taxa using molecular tools. Vavilov’s botanical study (1922) launched comparative genetic analysis as he pointed out that homology of characters is probably associated with homologous genes. The identifi cation of homologous genes from different species encountered diffi culties at that time but modern powerful technologies make homologous gene identifi cation easier and confi rmed Vavilov’s insight. Depending on the degree of their evolutionary relationship, different species preserve similarities in the content, proximity (synteny) and linear order (colinearity) of genes in their genomes. The pattern is consistent with similarity by descent; that it becomes increasingly disrupted as time passes. The preserved conservation of gene order is clear in vertebrates (Thomas and Touchman 2002; Ferguson-Smith and Trifonov 2007; Kemkemer et al. 2009) following hundreds of millions years of divergence. Comparing the genomes of fl owering plants is often problematic mainly due to the frequent polyploidization events in ancient plant genomes and consecutive gene loss (Bowers et al. 2003).
