diff --git a/pyham/abstractgene.py b/pyham/abstractgene.py
index 0f58531..b96819b 100644
--- a/pyham/abstractgene.py
+++ b/pyham/abstractgene.py
@@ -502,7 +502,6 @@ def set_MRCA(self):
 
         else:
             self.MRCA = self.ham._get_ancestral_genome_by_mrca_of_genome_set(children_genomes)
-            self.MRCA = self.ham._get_ancestral_genome_by_taxon(self.MRCA.taxon.up)
 
     def add_child(self, child):
         """
diff --git a/pyham/ham.py b/pyham/ham.py
index d5b3a1b..f955f53 100644
--- a/pyham/ham.py
+++ b/pyham/ham.py
@@ -902,11 +902,12 @@ def _get_ancestral_genome_by_taxon(self, tax_node):
                 :obj:`AncestralGenome`
 
         """
-
-        if "genome" in tax_node.features:
+        #make sure genome is ancestral genome
+        if "genome" in tax_node.features and isinstance(tax_node.genome, AncestralGenome):
             return tax_node.genome
-
+        
         else:
+        #create genome or overwrite extant genome with ancestral genome
             ancestral_genome = AncestralGenome()
             self.taxonomy.add_genome_to_node(tax_node, ancestral_genome)