1
$\begingroup$

I am working with a gene cluster found in several species. The genes involved are pretty much the same, with the odd insertion, but they can be often found in different orientations. So, I can't just do a multiple alignment of the whole cluster. I've done phylogenies of individual genes and I've looked at cluster architecture (indels, rearrangements) and things make sense (eg. limited HGT), but..

...Is there a simpler way to do this? A way to calculate / represent a phylogeny of the whole cluster? Like...some sort of web, maybe? Most of the software that does take rearrangements into consideration is meant for whole genomes, and is unreliable when it comes to fragments about 20-30kb long (like mine).

Thank you for your help!

$\endgroup$
  • 1
    $\begingroup$ Can you give us some example data? It's kind of hard to understand what you're looking at. Are you trying to build a phylogeny based on the entire cluster or have you separated each species' cluster into a multifasta file with each gene separate? If you haven't, wouldn't that be a reasonable approach? $\endgroup$ – terdon Aug 14 '19 at 12:27
  • $\begingroup$ If there'd be a way to build a phylogeny based on the entire cluster (that can deal with indels/inversions/rearrangements), I'd love to know it. I guess I could separate each species' cluster into a multifasta file, but I'm not sure what I could do after that? Could you please explain? It's unfortunate, because I'd lose positional information (eg. let's say species X is closely related to species Y and less so to species Z. In X and Y, the genes are in the order A-B-C-D, in Z they're in the order A-D-C-B), but if it's the only way... $\endgroup$ – Laura Aug 14 '19 at 13:41
  • $\begingroup$ Well, I don't really think the order will make much of a change in the phylogeny. I'd just use the multifasta approach to build the tree and then maybe annotate it with the directionality. $\endgroup$ – terdon Aug 14 '19 at 17:48
  • $\begingroup$ Its easy ... I strongly suspect these are bacteria ...please confirm. The likely application is resistance cassettes again please confirm. Finally this is likely a "genetic island" rather than a single gene ... again please confirm. $\endgroup$ – Michael Aug 14 '19 at 18:10
  • $\begingroup$ @terdon - Thank you. I've never built trees with multiple genes at a time, before. Could you recommend some software for it, please? Until now I've mostly used Seaview and the CIPRES webserver. $\endgroup$ – Laura Aug 15 '19 at 9:48
0
$\begingroup$

Firstly you wanted a webserver to build a tree, ok, I would use PhyML server. The good thing is that with only 22 taxa the calculations are easily doable.

What I'm assuming is you can map your rearrangements to produce a single homologous gene alignment for all taxa. So you appear to infer you can break your 20-30kb contig into individual aligments of homologous genes which has incorporated the rearrangement and enables easy production of an alignment file. This would leave you with around 20-30 gene alignment files. I hope that is correct, because that is how you get around the rearrangement problem and enables the data to be reassembled for the final tree (below).

Doing the tree is simple, because you can exploit the assumptions used in tree building regarding independence between mutations at each alignment position. The theoretical proof, the data is sound, is complicated. In summary,

  • build a consensus phylogeny (one tree representative of lots of trees) using two different approaches
  • combine the data into a single alignment, if the above looks good, or excluding the alignments that are affected recombination.

The theoretical issues with what you want to do are complicated because you need to distinguish bifurcating (clonal) homologues from recombination that could have occured in the reassortment events. The following is a purists approach, you might not want to do this stuff, but it gives you some idea.

Just before I do that ... I just want to check the alignments assumption is correct? and which bacteria?

| improve this answer | |
$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.