After hundreds or even thousands of generations both alleles for sickle cell anemia are still common in those of African ancestry. This is supported by two mechanisms: heterozygote advantage and gene flow.
Heterozygote advantage
When an allele is said to be heterozygous, it is carrying one copy of a gene. For example if one carries a copy of sickle cell allele, it will stay in the population even after many generations — natural selection will not be able to remove it and it will be passed on through generations. So, having one copy of that allele is advantageous but not deleterious.
Gene flow
With humans migrating throughout the different parts of the world, sickle cell allele is passed from one person to another or in different populations. It is actually advantageous to have one copy of this allele especially if there’s malaria in the area, which the allele is resistant.
The answer is; in the stroma. The chloroplast is the organelle inside the plant cell that performs the process of photosynthesis. Photosynthesis contains two kinds of reactions, the first is the light reactions which happen in the grana as it contains chlorophyll which absorbs light energy. The products of the light reactions are used to fix carbon dioxide in the second reactions which are the dark reactions. The dark reactions happen in the stroma outside the grana. Therefore, the stroma contains more carbon.
