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A common example of homologous structures is the forelimbs of vertebrates, where the wings of bats and birds, the arms of primates, the front flippers of whales, and the forelegs of four-legged vertebrates like horses and crocodilians are all derived from the same ancestral tetrapod structure.
Insect mouthparts show a multitude of different functional mechanisms across the wide diversity of insect species. It is common for significant homology to be conserved, with matching structures forming from matching primordia, and having the same evolutionary origin.
The recurrent evolution of flight is a classic example, as flying insects, birds, pterosaurs, and bats have independently evolved the useful capacity of flight. Functionally similar features that have arisen through convergent evolution are analogous , whereas homologous structures or traits have a common origin but can have dissimilar functions.
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.
For example, just by position one can identify species, albeit to a much lesser extent. Though most insects fold their wings when at rest, dragonflies and some damselflies rest with their wings spread out horizontally, while groups such as the caddisflies, stoneflies, alderflies, and lacewings hold their wings sloped roof-like over their backs ...
For example, the extinct trilobites had three tagmata: the cephalon (meaning head), the thorax (literally meaning chest, but in this application referring to the mid-portion of the body), and the pygidium (meaning rump). The Hexapoda, including insects, also have three tagmata, usually termed the head, thorax, and abdomen.
The same Hox protein can act as a repressor at one gene and an activator at another. The ability of Hox proteins to bind DNA is conferred by a part of the protein referred to as the homeodomain . The homeodomain is a 60- amino-acid -long DNA-binding domain (encoded by its corresponding 180- base-pair DNA sequence, the homeobox).
Convergent evolution is the development of analogous structures that occurs in different species as a result of those two species facing similar environmental pressures and adapting in similar ways. It differs from divergent evolution as the species involved do not descend from a closely related common ancestor and the traits accumulated are ...