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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.
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.
Sequences are either homologous or not. [3] This involves that the term "percent homology" is a misnomer. [4] As with morphological and anatomical structures, sequence similarity might occur because of convergent evolution, or, as with shorter sequences, by chance, meaning
Another method is to identify homologous sequences based on other known gene sequences (Tools see Table 4.3). [39] The two methods described here are focused on the sequence. However, the shape feature of these molecules such as DNA and protein have also been studied and proposed to have an equivalent, if not higher, influence on the behaviors ...
Conversely, the individual families that make up a superfamily are defined on the basis of their sequence alignment, for example the C04 protease family within the PA clan. Nevertheless, sequence similarity is the most commonly used form of evidence to infer relatedness, since the number of known sequences vastly outnumbers the number of known ...
In 2010, a team led by Edward Marcotte developed an algorithm that identifies deeply homologous genetic modules in unicellular organisms, plants, and animals based on phenotypes (such as traits and developmental defects). The technique aligns phenotypes across organisms based on orthology (a type of homology) of genes involved in the phenotypes ...
A pair of homologous chromosomes, or homologs, is a set of one maternal and one paternal chromosome that pair up with each other inside a cell during fertilization. Homologs have the same genes in the same loci , where they provide points along each chromosome that enable a pair of chromosomes to align correctly with each other before ...
When structures in different species are believed to exist and develop as a result of common, inherited genetic pathways, those structures are termed homologous. For example, the leaves of pine, oak, and cabbage all look very different, but share certain basic structures and arrangement of parts. The homology of leaves is an easy conclusion to ...