Table 2.   Types of Molecular Homology Homolog Genes that are descended from a common ancestor (e.g., all globins) Ortholog Homologous genes that have diverged from each other after speciation events (e.g., human - and chimp -globin) Paralog Homologous genes that have diverged from each other after gene duplication events (e.g., - and -globin) Xenolog Homologous genes that have diverged from each other after lateral gene transfer events (e.g., antibiotic resistance genes in bacteria) Positional homology Common ancestry of specific amino acid or nucleotide positions in different genes