Sacerdot C, Louis A, Bon C, Berthelot C, Roest Crollius H.

Genome Biol. 2018 Oct 17;19(1):166. doi:10.1186/s13059-018-1559-1

Chromosome evolution at the origin of the ancestral vertebrate genome.

“The pre-1R karyotype comprised 17 chromosomes, duplicated into 34 chromosomes after the first WGD and followed by seven fusions. The resulting 27 chromosomes were duplicated in the second WGD leading to 54 Vertebrata chromosomes, at the origin of the approximately 60,000 extant species of vertebrates.” “The 54 chromosomes in the post-2R Vertebrata led to a Euteleostomi karyotype of 50 chromosomes (4 fusions) and to an Amniota karyotype of 49 chromosomes.” “The structure of the 17 pre-1R chromosomes is still strikingly apparent in the human genome, with some chromosomes almost entirely composed of genes from a single pre-1R chromosome (e.g., chromosomes 14 and 15).“ “We note that although all chromosome tetrads corresponding to pre-1R chromosomes are complete (i.e., are composed of 4 CARs), the 49 reconstructed Amniota chromosomes display large differences in gene numbers: the largest contains 862 genes (chromosome 37) and the smallest only 16 genes (chromosome 49). This could reflect either a more intense process of gene inactivation and loss on chromosomes with fewer genes, or a more intense rate of rearrangement on those chromosomes, leading to greater difficulties in reconstructing them.“