Similarity in the sequence of a protein or nucleic acid or in the structure of an organ that reflects a common evolutionary origin. Molecules or sequences that exhibit homology are referred to as homologs. In contrast, analogy is a similarity in structure or function that does not reflect a common evolutionary origin.
An observable characteristic of an organism that arises from environmental factors, or a combination of environmental and genetic (genotype) factors. Organisms with the same genotype can have very different phenotypes.