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.
I think the answer is the Eukaryote Kingdom. I hope this helps (:
The right answer is spongy bone (cancellous bone).
In otosclerosis, the new bone blocks the movement of the stirrup, causing transmission hypoacusia. Otosclerosis can also cause perceptive deafness, especially when otosclerotic bone foci are close to scala media. Half of all cases are hereditary. The measles virus may play a role in triggering a genetic predisposition to otosclerosis.
