Figure 26.13: A gene tree can be used to represent the evolutionary relationships among a group of genes. This gene tree is a rooted tree, in which PRL represents a prolactin gene; PRL1 and PRL2 are two different prolactin genes found in the same organism; and SOMA represents a somatropin gene, which is related to prolactin genes.
[After M. P. Simmons and J. V. Freudestein, Uninode coding vs. gene tree parsimony for phylogenetic reconstruction using duplicate genes, Molecular Phylogenetics and Evolution 23:488, 2002.]