Why are eukaryotes not immune from genetic mutations during cell reproduction?

Answer 1

This is a good question with a rather complicated answer.

The reason for mutation is that everything is down to probabilities. Every time a base is being added there is a chance that the wrong base could be added. This process produces changes in the genetic code. However this doesn't always lead to a propper mutation. The cell has many different ways of detecting mismatches or bulky adducts etc. and many ways of fixing these changes. Even when a mutation manages to avoid these systems there is a good chance that the mutation will be a synonomous mutation ie. there is no change in the amino acid in the protein or binding of a miRNA. However the sheer number of the mutations means that damaging mutations still get past.

You might think that since mutations are so bad in humans that mutation is bad in general, and most of the time you'd be right. However think of a primitive proto-cell. These would not have worked efficiently in any way, so damaging mutations would likely have been less detrimental to survival. More than that the sheer number of them would mean that even in a new cell had a lethal mutation enough of them would survive. However their mutation rate would prove an advantage in that many of the mutations would be beneficial to the species.

Mutations are actually beneficial in many ways. The HLA loci in humans actually mutates ar a very high rate and that is beneficial.

So as to why we are not immune to mutation; mutation is essential for the survival of a species. Without mutation there would be no natural selection and once a species came up against an environment inimical to it, it would die. With mutation some of the organisms will usually have mutations making them better adapted to the environment, and they will survive. Most of their descendents will have the trait and those that don't will usually not survive and the trait will eventually become fixed in the population.