Homology Examples
From Indipedia: India's Wikipedia at OSDD
[edit] Homology Examples
Homology refers to any similarity between characteristics that is due to their shared ancestry.There are examples in different branches of biology. Anatomical structures that perform the same function in different biological species and evolved from the same structure in some ancestor species are homologous. In genetics, homology can be observed in DNA sequences that code for proteins (genes) and in noncoding DNA. For protein coding genes, one can compare translated amino-acid sequences of different genes. Sequence homology may also indicate common function. Homologous chromosomes are chromosomes with the same genes, but non-identical nucleotide sequences that can pair (synapse) during meiosis, and are believed to share common ancestry.
Examples
1.Lysozyme,an enzyme that catalyses the hydrolysis of bacterial cell wall polysaccharides, which share around 50% identity(70% similarity) with alpha-Lactalbumin, a non-catalytic regulatory milk protein whose presence in required for lactose synthase to transfer a galactose molecule from UDP-galactose to D-glucose.In spite of this high level of sequence similarity, and highly similar folds, the function of protein differ in the two key catalytic residues of lysozyme(glutamic and aspartic acid)that are not conserved in alpha-lactalbumin and the acidic calcium binding motif characteristic of alpha-lactalbumins are shared by only few lysozyme.
2.Rhodopsin-like super family of G-protein-coupled receptors.These proteins which includes light, olfactory, gustatory, hormone and neurotransmitter receptor, encompass a wide variety of functions. The emergence of different specificities and function following gene duplication events may be detected by protein sequence comparison. For example, different visual receptors(opsins), which diverged from each other early in vertebrate evolution, are stimulated by different wavelength of light.Human long wavelength opsins(i.e those sensitive to red and green light) are more closely related to each other(with around 95% sequence identity) than either sequence is to the short wavelength blue opsins, or to the rhodopsin(achromatic receptors) with which they share an average 43% identity.
