Putnam NH, Butts T, Ferrier DE, Furlong RF, Hellsten U, Kawashima T, Robinson-Rechavi M, Shoguchi E, Terry A, Yu JK, Benito-Gutiérrez EL, Dubchak I, Garcia-Fernàndez J, Gibson-Brown JJ, Grigoriev IV, Horton AC, de Jong PJ, Jurka J, Kapitonov VV, Kohara Y, Kuroki Y, Lindquist E, Lucas S, Osoegawa K, Pennacchio LA, Salamov AA, Satou Y, Sauka-Spengler T, Schmutz J, Shin-I T, Toyoda A, Bronner-Fraser M, Fujiyama A, Holland LZ, Holland PW, Satoh N, Rokhsar DS.

Nature. 2008 Jun 19;453(7198):1064-71. doi:10.1038/nature06967

The amphioxus genome and the evolution of the chordate karyotype.

17 ancestral chordate chromosomes.

“We estimate that the haploid amphioxus genome contains 21,900 protein-coding loci. [...] The observed heterozygosity shows correlations at short distances that decay on scales greater than ∼1 kb, indicating extensive recombination in the population. [...] Wwe reconstructed the gene complements of 17 linkage groups (that is, proto-chromosomes) of the last common chordate ancestor. [...] This analysis shows that most of the human genome (112 segments spanning 2.68 Gb, or 95% of the euchromatic genome) was affected by large-scale duplication events on the vertebrate stem before the bony vertebrate radiation (that is, the teleost/tetrapod split), and that nearly all of the ancient chordate chromosomes were quadruplicated. [...] Allowing for a range of nearly parsimonious reconstructions of 2R, we estimate that the bony vertebrate ancestor had between 37 and 49 chromosomes.”