Table 1.
Main cytogenomic traits in fish-like chordates.
| Group | 2n Chromosome Counts (Basic Features) | Micro- Chromosomes | CG Heterogeneity | WGD after the First Two Basal Vertebrates´ WGDs | C-value/Haploid DNA Content (pg) [12] | Specific Features in the Genome History and Chromosomal Evolution |
|---|---|---|---|---|---|---|
| Myxiniformes (hagfishes) | 14–48 | NO | unknown | not observed | Myxinidae 2.5–4.59 | chromatin diminution, programmed genome rearrengement [13,14] |
| Petromyzontiformes (lampreys) | 76–178 | NO | GC-rich DNA repeats | not observed | Petromyzontidae 1.29–2.5 | programmed genome rearrengement [14] |
| Chondrichthyes (cartilaginous fishes) | 54–102 | YES | observed, presumably satellite DNA | not observed | Chimeriformes 1.5-2 Selachimorpha ~3–17 Rajimorphii 2.7–17 | AT/GC heterogeneity positively correlated with genome size [15] |
| Ceratodontiformes (lungfishes) | 34–68 | Only N. forsteri [15] otherwise not | unknown | not observed |
Neoceradotus 52.75–74.86 Lepidosiren 80.55–123.9 Protopterus 40–132.8 |
“genomic obesity” without WGD documented [16,17] |
| Coelacanthiformes (lobe-finned fishes) | 48 | YES | unknown | not observed | Latimeria 2.8–6.6 | chromosomes similar to ancient frogs [18] |
| Acipenseriformes (sturgeons, paddlefish) | ~ 120–240–360 | YES ~ 50% | NORs and GC-rich microchromosomes [7] andG-banding [19,20] | multiple in sturgeons, one in paddlefish |
Acipenser 1.8–9.3 Polyodon 1.6–2.4 |
multiple WGD, ploidy diversity |
| Lepisosteiformes (gars) | 56–58 | small sized chromosomes | in both genera | not observed |
Atractosteus 1.2 Lepisosteus 1.4 |
regionally high recombination rate |
| Amiiformes (bowfin) | 46 | NO | only NORs | not observed | Amia calva 1.2 | convergent evolution with teleosts? |
| Polypteriformes (bichirs) | 36–38 biarmed, extremelly large | NO | only NORs | not observed |
Erpetoichthys 4.5 Polypterus 3.6-7.2 |
not investigated |
| Teleostei | ~ 50 (exceptions up to 100–150 or more) | Micro B-chromosomes | only NORs | TGD and lineage specific WGDs | mostly 0.4- ~ 1.0 | from genome compaction to lineage specific WGD |
WGD: Whole-genome duplication; NOR: Nucleolar organizer region; pg: picograms.
a orders and families mostly based on [22]; b c-value, based on [12] database; c n: based on genomic/sequence data, originates from NCBI, 2n based on cytogenetic data [86]; d number of assemblies currently released and level of assembly (C = contig, D = draft, S = scaffold, Ch = chromosomal level); e Sequencing methods (I = Illumina, PB = PacBio, S = Sanger), linkage map (LM) available.