Question

Part A: The MC1R (melanocortin 1 receptor) gene is responsible for normal pigmentation of skin in humans and controls which kind of melanin is made by skin cells, eumelanin and/or pheomelanin. Melanin serves as a cover for the cells so harmful UV rays cannot reach the nucleus and cause mutation, but also protects folate, a type of B vitamin essential in growth and metabolism. However, there are two sides to this story: exposure to sunlight is required to convert calcium to Vitamin D, an important molecule in bone growth and absorption of essential nutrients.

1. At what latitudes would you expect to find human populations with the highest levels of the two melanin pigments in their skin? Why? Predict the diversity of the MC1R gene in these populations (high/low) and why you might expect this pattern.

Answer 1

populations with darker skin color (more eumelanin) would be found in regions with more intense UV radiation. Thus, populations found in equatorial areas will have the darkest skin (most eumelanin) and populations at higher latitudes will have lighter skin (least eumelanin). in contrast, The increased frequency of blonde or red-haired individuals at higher latitudes suggests that favoring pheomelanin over eumelanin production results in increased UVR penetration permitting more efficient UV-dependent transformation of circulating precursors in the skin, which is the essential first step of vitamin D synthesis.

The gene MC1R exhibits reduced diversity in African populations from high UVR regions compared to low-UVR non-African populations DUE TO selection to maintain darker skin in high UVR environments is expected to constrain pigmentation phenotype and variation in pigmentation loci. MC1R amino acid variants observed in non-African populations do affect MC1R function and contribute to high levels of MC1R diversity in Europeans countries.