Chromosomal Relationship Between Member Species of Genus Salmo

Whole genome duplication (WGD), which occurred in 95 Mya in the common ancestor of extant salmonids resulted in doubling the chromosome complement along with all the genes. Following the ancestral duplication event, chromosomal rearrangements including Robertsonian fusions and translocations are believed to be the primary means to achieve the re-diploidization of salmonid genomes, where the unstable polyploid genome begins to reduce to a more stable diploid form. To further elucidate the mechanism of this complex chromosomal relationship, we performed a comparative cytogenetic analysis of the chromosomal architecture between two sole members of the Salmo genus, Atlantic salmon (Salmo salar) and brown trout (Salmotrutta). To avoid interference from chromosomal variations detected in North American populations, the European subspecies of Atlantic salmon was chosen for this project. The karyotype complement of European Atlantic salmon comprises of 58 chromosomes (8 pairs of metacentric and 21 pairs of acrocentric chromosomes) with the number of chromosome arms (NF) of 74, whereas brown trout has 80 chromosomes (11 pairs of metacentric and 29 pairs of acrocentric chromosomes) with a NF of 100. Through Fluorescent in-situ hybridization (FISH) using BAC probes representing different sections of Atlantic salmon chromosomes, multiple ancestral fusions was observed in Atlantic salmon chromosomes, explaining the significant reduction in chromosomes seen in Atlantic salmon when comparing to the brown trout.