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Document Type

Thesis - University Access Only

Award Date


Degree Name

Master of Science (MS)

Department / School


First Advisor

Nels H. Granholm


The aesthetic and functional variety of mammalian pigmentation attracted scientific investigation at the beginning of the century as W.E. Castle, L.C. Dunn, and others-initiated studies on coat color inheritance in rabbits, guinea pigs, rats, and mice. Breeding experiments and gross observation of chromosomal abnormalities by early researchers led to hypotheses suggesting linkage between the genes whose products were responsible for variation of coat color in rats and mice. " .... Although these investigators were completely unaware of the anatomical basis of pigmentation, not to mention its biochemistry, their studies clearly established that the production of coat-color patterns involved a local interaction of specific gene products which was relatively unaffected by systemic or environmental factors". The groundwork having been completed, subsequent research was aimed at characterizing the means by which the gene products interacted to produce pigment, a process to be known as melanogenesis. M.E. Rawles was the first to produce evidence that melanin was produced from highly dendritic cells of neural crest origin now known as melanocytes. Further study established that the melanocytes of mammalian skin and hair contained subcellular granules, called melanosomes, in their cytoplasm that synthesized melanin. Fully melanized melanosomes are transported into the dendritic arms of the melanocyte where keratinocytes phagocytize the ends of the dendritic projections and engulf the pigmented granule, thereby giving color to the skin and hair. The functional understanding of melanogenesis at the cellular level, in concert with the fact that melanin production occurs in response to specific gene products within an easily visualized, discrete organelle, led to extensive research on the physiological genetics of pigmentation. Indeed, the melanocyte has become a widely used model for elucidation of how genes, responsible for the processes of melanogenesis, produce their effects. Mutations may be described as "experiments of nature" where new phenotypes evolve as genes are deleted and/or rearranged in response to a specific environmental stress. Both natural and induced (chemical and radiation) mutations are of great value to the researcher interested in the effects of specific gene products on a physiological process " ... since the influence or influences of a specific gene locus can be established only on the basis of variations (alleles) from the wild type that have been produced by mutations. Mutations give rise to alleles which not only identify the locus but which, on the basis of their effects, tell us something about the kind of activity with which the locus is involved".

Library of Congress Subject Headings

Phenol oxidase



Melanins -- Synthesis



Number of Pages



South Dakota State University