The Drosophila Histone Cluster is a gene cluster that contains more than a hundred copies of a sequence that encodes several histone proteins. These copies are very similar.
My question is what mechanism are known that could have played a role in the genesis of this cluster?
I'm aware of the possibility of recombination, which might expand the cluster on one chromosome, shortening it on the other. Are there any other mechanisms to expand or change the cluster and are there telltale signs left by these mechanisms in the genome sequence?
Given that in most species histone genes aren't clustered, it would be weird to assume that recombination is the only mechanism to duplicate these sequences. Also, at one end of the cluster bits and pieces of histone genes are mixed with other sequences, a bit like all the broken copies got pushed to one end. It would be interesting to have an explanation for this pattern.