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.
A population that has been isolated, especially a smaller one, could have a high level of homozygosity and therefore not a lot of genetic variation. Gene flow between such populations can increase the level of heterozygosity, and therefore up genetic variation.
That is when extinction occurs. Hope I helped!
Answer:
The correct answer is option c) "It is necessary to have a completely functioning pentose phosphate pathway for a tissue to synthesize ribose phosphates".
Explanation:
While the pentose phosphate pathway is the most common way at which a tissue synthesize ribose phosphate, it is false to affirm that it is necessary for ribose phosphate synthesis. Tissues have alternatives to the pentose phosphate pathway to synthesize ribose phosphate. For instance, the nucleotide salvage or the salvage pathway allows tissues to synthesize ribose phosphate from intermediates in the degradative pathway for nucleotides.