A primary structural protein in the human body, collagen is found in the skin, bones, joints, connective tissues, and blood vessels. (healthadviceworld.com)
The trait appears to be genetic and is a result of variation in collagen, the main structural protein of connective tissue. (scientificamerican.com)
As structural proteins, they are involved in the growth of tissue, such as nails or hairs. (sciencedaily.com)