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As with anatomical structures, sequence homology between protein or DNA sequences is defined in terms of shared ancestry. Two segments of DNA can have shared ancestry because of either a speciation event or a duplication event . Homology among proteins or DNA is typically inferred from their sequence similarity.
All vertebrate forelimbs are homologous, meaning that they all evolved from the same structures. For example, the flipper of a turtle or of a dolphin , the arm of a human, the foreleg of a horse, and the wings of both bats and birds are ultimately homologous, despite the large differences between them.
A phenome is the set of all traits expressed by a cell, tissue, organ, organism, or species. The term was first used by Davis in 1949, "We here propose the name phenome for the sum total of extragenic, non-autoreproductive portions of the cell, whether cytoplasmic or nuclear.
Comparative anatomy is the study of similarities and differences in the anatomy of different species. It is closely related to evolutionary biology and phylogeny [ 1 ] (the evolution of species). The science began in the classical era , continuing in the early modern period with work by Pierre Belon who noted the similarities of the skeletons ...
Arrows show the vestigial structure called Darwin's tubercle. In the context of human evolution, vestigiality involves those traits occurring in humans that have lost all or most of their original function through evolution. Although structures called vestigial often appear functionless, they may retain lesser functions or develop minor new ones.
On the trunk of the body, the chest is referred to as the thoracic area. The shoulder in general is the acromial, while the curve of the shoulder is the deltoid. The back as a general area is the dorsum or dorsal area, and the lower back as the lumbus or lumbar region. The shoulderblades are the scapular area and the breastbone is the sternal ...
Hox genes, a subset of homeobox genes, are a group of related genes that specify regions of the body plan of an embryo along the head-tail axis of animals. Hox proteins encode and specify the characteristics of 'position', ensuring that the correct structures form in the correct places of the body.
The pattern of limb bones called pentadactyl limb is an example of homologous structures (Fig. 2e). It is found in all classes of tetrapods ( i.e. from amphibians to mammals ). It can even be traced back to the fins of certain fossil fishes from which the first amphibians evolved such as tiktaalik .