Answer:
Because natural selection selects for it. Thus it persists.
Explanation:
You have to understand heterozygote advantage. Basically, it's where heterozygotes have an advantage over homozygotes. In the case of sickle cell disease, heterozygotes have an advantage, and natural selection favors whatever is advantageous. Thus, because heterozygotes each have one recessive sickle-cell allele, as natural selection favors the heterozygotes, the recessive sickle-cell allele persists and remains in the gene pool.
Serious systemic fungal infections and parasitic infections usually only develop in individuals who are immunocompromised. These individuals have a weak immune system. The body cannot respond quickly to infections since their immunity is not very well developed.
Answer:
ER → ER-to-Golgi transport vesicles → Golgi cisternae → secretory or transport vesicles →cell surface (exocytosis) (see Figure 17-13). Small transport vesicles bud off from the ER and fuse to form the cis-Golgi reticulum.
They occurred in industrialized areas.
