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docs/tutorials/003_gene_families_trees.md

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 # Tutorial: Gene families and Phylogenetic Trees
 
+Homologous genes (genes derived from a common ancestor) are usually group into gene families. Orthologs, genes derived
+from a common ancestor through speciation, are similarly grouped into OrthoGroups. CoNekT supports 
+[tribeMCL](https://www.ncbi.nlm.nih.gov/pubmed/11917018) and [OrthoFinder](https://github.com/davidemms/OrthoFinder) for 
+Homologous groups and OrthoGroups respectively.
+
 ## Gene Families
 
 
-## Phylogenetic Trees
+
+
+## Phylogenetic Trees
+
+Phylogenetic Trees generated by [OrthoFinder](https://github.com/davidemms/OrthoFinder) can be imported into CoNekT. These
+can be accessed from gene pages for sequences included in the tree or the corresponding gene family page. 
+
+A unique feature of CoNekT is that conditions can be manually curated per species and expression levels of genes in 
+comparable tissues/organs can be added to the phylogenetic tree. This allows for changes in expression patterns between
+duplicated genes or after speciation events to be visualized. 
+
+![phylogenetic tree](images/phylo_tree_example.png "Phylogenetic tree example") 
+
+In the example above various genes related with cellulose synthase (an important component of plant cell walls) is shown.
+Here it is immediately clear that some groups of cellulose syntases are specific for leaves while others play a role in 
+reproductive structure.