Answer:
Genetic, geographic & cultural factors that cause sickle-cell anemia. It is important to note that even genetic diseases are caused by multiple social, environmental and biological factors. This is particularly true in the case of sickle-cell anemia, a genetically inherited blood disorder usually found in people with West African ancestry (PBS 2001).
I think it's the first and second option but I could be wrong because I don't know much about deserts :)
Phospholipids have two distinct polarities. The phosphate head is always polar, while the two "tails" it has are nonpolar.
