"Schematic outline of melanogenesis. UVR stimulates the expression of POMC by keratinocytes. The peptide produced is the precursor of the hormone a-MSH, that binds to MC1R in melanocytes. This union leads to an increase in cellular cyclic adenosine monophosphate (cAMP) that in turn leads to increased levels of MITF expression, which upregulates the transcription of TYR, TYRP1 and TYRP2, producing brown-black eumelanin. In the absence of a-MSH, the antagonist ASIP binds to MC1R, and phaeomelanin is synthetized instead. Melanosomes are then transferred to keratinocytes through the dendrites via a shedding vesicle system."   Briefly discuss how these several aspects of the molecular and cellular biology of melanin production and melanosome transfer contribute to determine skin color. How would different mutations in the hormonal response to ultraviolet light, the melanin production signal transduction pathways, and melanosome transfer influence skin color, hair color, and eye color? Did this study change what you knew about such human phenotypic variations?

"Schematic outline of melanogenesis. UVR stimulates the expression of POMC by keratinocytes. The peptide produced is the precursor of the hormone a-MSH, that binds to MC1R in melanocytes. This union leads to an increase in cellular cyclic adenosine monophosphate (cAMP) that in turn leads to increased levels of MITF expression, which upregulates the transcription of TYR, TYRP1 and TYRP2, producing brown-black eumelanin. In the absence of a-MSH, the antagonist ASIP binds to MC1R, and phaeomelanin is synthetized instead. Melanosomes are then transferred to keratinocytes through the dendrites via a shedding vesicle system."

Briefly discuss how these several aspects of the molecular and cellular biology of melanin production and melanosome transfer contribute to determine skin color. How would different mutations in the hormonal response to ultraviolet light, the melanin production signal transduction pathways, and melanosome transfer influence skin color, hair color, and eye color? Did this study change what you knew about such human phenotypic variations?