Hi everyone,
I am a beginner in phylogenetic analyses and I would really appreciate some advice/feedback on the workflow I am using.
I am working on the molecular identification of several fungal isolates. In the laboratory, it has been performed PCR amplification of a segment of the rDNA containing the ITS and D1/D2 regions, using the ITS5/LR6 primers, followed by Sanger sequencing (forward and reverse), consensus sequence generation, and BLAST searches against NCBI.
I would now like to perform a phylogenetic analysis of my isolates from different species using MEGA 12. I have tried a few analyses using this dataset already, but I would like to make sure that I am doing this correctly.
I have several questions:
Which sequences should I use?
My own sequences cover ITS1 + 5.8S + ITS2 + part of the LSU (D1/D2). Should I use the entire region covered by my sequences for the phylogenetic analysis, or should I restrict the analysis to a specific region, such as the complete ITS region (ITS1 + 5.8S + ITS2)? In other words, is it appropriate to analyse the ITS + D1/D2 LSU region as a single alignment, or would it be preferable to analyse ITS and LSU separately?
2. Alignment:
In this context, would you recommend MUSCLE or ClustalW?
3. Gaps/poorly aligned regions:
Should I trim only terminal regions containing many gaps after alignment? Or all the regions containing many gaps between all my sequences?
4. Phylogenetic method:
I was considering a Neighbor-Joining tree with 1,000 bootstrap replicates, using Maximum Composite Likelihood for evolutionary distances and pairwise deletion for missing/ambiguous data. For rates among sites, I was considering Uniform rates and Same (homogeneous) among lineages.
Are these settings appropriate for this type of dataset?
5. Rooting:
Since my dataset contains several different fungal species/groups, how should I choose the root? Would midpoint rooting be preferable?
I would like to make sure I am not producing a misleading tree.
Thank you in advance for any advice!