We’re doing it for the children!
The basic misconception in this question is that the important effects of mutations are seen in the cell that undergoes mutation. This is not the case. So focusing on the whether the strand that receives a mutation is the non-transcribed, sense, strand or the transcribed (anti-sense) strand is of little relevance.
What is important is whether or not the mutation is passed on to the progeny.
Don’t we have a life too?
Why isn’t it important? Consider a mutation occurring in a single E. coli cell in a population of millions of E. coli, or a single muscle cell in a human muscle. Even if there is a mutation in the strand that is transcribed into mRNA and translated into protein, the change in that one cell will not have a significant effect on the overall population.
The birds and the bees
The way in which a mutation — on sense or anti-sense strand — can affect a population of bacterial cells or whole tissue in an organism is:
- (For bacteria or in tumour cells) if the mutation is passed on to some of progeny, which then have a selective advantage so that they can outgrow the wild-type population
- (For normal tissues in animals) if the mutation is passed on to the progeny through the germ line so that it is present in all (e.g. muscle) cells
Still harking on about sex (Yawn)
The key point is easier to explain with bacteria. Consider a simplistic situation in which a mutation occurs on one strand (and is not corrected by the DNA-repair mechanisms). Before the cells divide into two daughter cells the double-stranded DNA replicates — each strand is the template for a complementary strand in a daughter double-stranded DNA. One cell will have the daughter dsDNA (double-stranded DNA) copied from the unmutated strand and the other will have the daughter dsDNA copied from the mutated strand.
In the case of the dsDNA copied from the mutated strand, both
strands will clearly carry the mutation, so it is irrelevant whether
the mutated strand in the parent was sense or anti-sense.
If the mutation is advantageous these cells will grow and divide and out-compete the other bacteria in the population.
A similar explanation holds for tumour cells in a differentiated animal tissue.
In the case of germ-line cells in animal tissues the situation is slightly different — the mutation either will be present or absent in both strands of the dsDNA in the fertilized egg, and so will affect all of the cells in the tissues of the progeny in which it is expressed.