homology (redirected from homolog)

homology (hōmŏl`əjē), in biology, the correspondence between structures of different species that is attributable to their evolutionary descent from a common ancestor. For example, the forelimbs of vertebrates, such as the wing of bird or bat, and the foreleg of an amphibian, are homologous; there is an almost identical number of bones in the limbs, and the pattern construction is identical. Homologous structures do not necessarily have to have the same function; the wings of birds and forelegs of a horse are homologous through they clearly serve different functions. Analogy is the functional similarity between structures that do not have a common origin; for example, the wings of birds and those of insects are analogous.

---

homology

Similarity of the structure, physiology, or development of different species of organisms based on their descent from a common evolutionary ancestor. Analogy, by contrast, is a functional similarity of structure that is based not on common evolutionary origins but on mere similarity of use. The forelimbs of such widely differing mammals as humans, bats, and deer are homologous; the form of construction and the number of bones in each are practically identical and represent adaptive modifications of the forelimb structure of their shared ancestor. The wings of birds and insects, on the other hand, are merely analogous; they are used for flight in both types of organisms but do not share a common ancestral origin.

---

homology

1. Chem the similarities in chemical behaviour shown by members of a homologous series

2. Zoology the measurable likenesses between animals, as used in grouping them according to the theory of cladistics