Subfunction partitioning, the teleost radiation and the annotation of the human genome

Six cadm/synCAM genes are expressed in the nervous system of developing zebrafish

“…In fact, three orthologous genes are found in all three chromosomal regions: jam3, igsf9b, and grit (Supplementary Figure S2). This confirms that cadm1a and 1b are derived from a duplication of the ancestral chromosomal region (Postlethwait et al, 2004).…”

“…In addition, the maintenance of the duplicated cadm1 and cadm2 loci in zebrafish indicates that multiple functions of the mammalian orthologs may have been partitioned to the co-orthologs. On the other hand, it is possible that the coorthologs may carry out the same function but in different tissues or at different times during development, as has been seen for other co-orthologs in teleost fish (Postlethwait et al, 2004).…”

“…plication before branching off from the tetrapod lineage during evolution (Postlethwait et al, 2004), we hypothesized that the genes similar to mouse Cadm1 and 2 are co-orthologs. We have named these cadm1a and cadm1b, and cadm2a and cadm2b.…”

“…Analysis of conserved synteny between phyla can provide evidence of orthology and is necessary to determine whether genes are duplicates arising from a genome duplication (Postlethwait et al, 2004). Radiation hybrid mapping determined that cadm1a, 1b, 2a, 2b, 3, and 4 map to linkage groups 21, 16, 2, 15, 10, and 15, respectively.…”

Zebrafish: A model system for the study of eye genetics

“…Comparative studies provide evidence of a genome wide duplication in the lineage of ray-finned fishes. Estimates suggest that for at least twenty percent of human genes the zebrafish has preserved two orthologues (reviewed in Postlethwait, et al, 2004). Though the initial assumptions held that the presence of two functional copies of a gene would mask the effects of mutations in one or the other, many of the zebrafish co-orthologues demonstrate subfunctionalization of the roles of the ancestral gene.…”