Patterns of conservation and diversity amongst tandemly repeated multigene families across mollusks

Gene duplication provides a potentially important source of genetic variation. Over time the copies created by duplication can evolve divergent nucleotide sequences and functions, resulting in clustered families of similar genes like the histone and rDNA genes. The gene families often continue duplicating and create regions of many identical tandem repeats of the whole gene cluster. Repeat clusters can have high copy number variation; examination of the New Zealand freshwater snail for example demonstrated asexually reproducing snails possessed hundreds of times more copies of rDNA and histone genes than their sexual counterparts. The research on the snail’s gene repeats also revealed a new discovery: The normally separate rDNA and histone clusters had combined into a single tandemly repeating unit in this species. This trait was never observed in other animal, not even the snail’s molluscan relatives. Previous histone gene examination in mussels suggested mollusks possess more dynamic and diverse histone gene clusters than other invertebrates. If mollusk histone gene arrangement is consistently varied, the snail’s unique arrangement and others like it could more common than initially though. To better understand the patterns of histone and rDNA arrangement and association, I collected high quality genome assemblies for a wide variety of mollusk phylum, retrieved the gene sequences, reconstructed the gene positions within a cluster, and then mapped different rearrangements and combinations of repeated genes on the molluscan family tree to assess which traits changed the most.