Collagen evolution of collagens was a fundamental step in the early evolution of life, supporting the coalescence of multicellular life forms. Collagen D-banding is viable as periodic formation of ridging on all fibrils forming collagen. D-bands are created due to the semi-crystalline formation of the collagen within the fibrils. The pattern exhibited by D-banding is consistently independent of fibril diameter. When undergoing deformation, collagen fibrils may lose their D-banding, making the disappearance of the d-bands an indicator of the type of damage undergone by then tendon fibrils. Collagen Collagen is the main structural protein in the extracellular space in the various
Keratin used as fluorescent markers to distinguish subsets of TECs in genetic studies of the thymus. Additionally, the baleen plates of filter-feeding whales are made of keratin. Keratins (also described as cytokeratins) are polymers of type I and type II intermediate filaments, which have only been found in the genomes of chordates (vertebrates, Amphioxus, urochordates). Nematodes and many other non-chordate animals seem to only have type VI intermediate filaments, lamins, which have a long rod domain (vs. a short rod domain for the keratins). The human genome encodes 54 functional keratin genes which are located in two clusters on chromosomes 12