Distribution of 2R proto-Actinopterygian ancestral chromosome affinities in the genome of three-spined stickleback ( Gasterosteus aculeatus ). Chromosomes are all acrocentric and are arranged with centromeres at the top. 2R ancestral chromosome designations follow the convention of Kasahara et al. (2007). Syntenic affinities are colour-coded as per the legend on the bottom left-hand corner. The size of each chromosome is denoted in millions of base-pairs at the bottom of each chromosome and was obtained from ENSEMBL v60.