Ans.
Sickle-cell disorder is a genetic disorder, which shows defected red blood cells, due to mutation in the genes for hemoglobin protein.
Malaria is common in sub-Saharan Africa region and there, natural selection favored gene for sickle cells, because it might be beneficial to people having sickle cell disease that makes them able to survive in such condition and transmit their genes to offspring.
On the other hand, in those Africans, who moved to United States, where malaria is uncommon or absent, natural selection favored normal, wild type genes, resulting in fewer people with defected sickle cell.
Hence, sub-Saharan African population shows higher percentage of mutated gene for sickle cell as compared to population of United States.
Thus, the evolutionary process behind this difference is 'natural selection.'
3x +12. Look at the picture below for the explanation!
Hope this helps!
Melanophores are small pigments that are present in the dermis layer of the skin of a shark. They impart a gray color to the dorsal and lateral surface area of the shark. They help in background adaptation and countershading of the body, which makes a shark difficult to be seen.
Lecithin is (organic chemistry) the principal phospholipid in animals; it is particularly abundant in egg yolks, and is extracted commercially from soy. It is also a major constituent of cell membranes, and is commonly used as a food additive (as an emulsifier). While cephalin is (biochemistry) a phospholipid found particularly in the cells of nervous tissue; it is also the primary phospholipid in bacteria.