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Several important issues can be addressed by looking at the figure above:


The phylogenic tree will vary in shape somewhat dependent on the parameters used for its generation, including whether protein sequence or DNA sequence is used to generate relationships. The phylogenic tree above was generated by Krakauer et. al. using amino acid sequence of the proteins (they also generated trees using DNA sequences). Only the protein tree is presented above. Although the gene (codon) tree has many advantages over the protein tree for visualizing evolutionary changes, the protein tree is the most useful in determining possible connections with the prion diseases as:

In the figure above, all species are members of the Kingdom:Animalia and Phylum:Chordata, but the chicken is a member of the Class:Aves whereas all other species are members of the Class:Mammalia (for reference a detailed description of some of the domestic animal species is shown in the figure below)

Phylogeny classification

Kingdom

Phylum (Subphylum)

Class (Subclass, Infraclass)

Order

Family (Subfamily)

Genus

species (subspecies)