...a neutral mutation will remain in a stable population in just one individual. Why? I don't think this needs to be the case as is shown here. Especially in small populations this can happen quite often.
Also, a beneficial mutation can occur directly and it doesn't necessarily need a neutral intermediary.
Yes, it would happen to an offspring. However, see above, a neutral mutation is highly unlikely to spread. My point though is that because you essentially would need all 5 mutations in this case, and the 3rd or 4th would kill the individual, you would never get to the 5th. Think about it.
But it doesn't happen that way. There is no planing ahead - if a mutation is detrimental, that's it. So all "modifications" have to work at least as good as the status quo.
Why? I don't think this needs to be the case as is shown here. Especially in small populations this can happen quite often.Hate to tell you, but it's wrong. Neutral mutations will almost certainly dissappear as shown below. And note that this is from an educational site, not from any kind of biased against evolution place:
- 1.
- The graph below summarizes the relationship between population size and probability of fixation of a favorable allele. In small populations the favorable allele has higher probability of fixation than in large populations (this is surprising!), whereas larger population size sees the probability of fixation approach a constant value about equal to
. The effect in small populations is like that for a neutral mutation, but as population size increases the chance of the neutral mutation reaching fixation diminishes. As a consequence, larger populations favor fixation of advantageous mutations compared to neutral mutations, as shown by the ratio of the fixation probability of advantageous to neutral mutations. Note that this does not include any information on the rate at which neutral or advantageous mutations occur. 
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- From: WSU Population Genetics
You can also check the same question in the 'bible' of evolution - TalkOrigins:
Neutral alleles Most neutral alleles are lost soon after they appear. The average time (in generations) until loss of a neutral allele is 2(Ne/N) ln(2N) where N is the effective population size (the number of individuals contributing to the next generation's gene pool) and N is the total population size. Only a small percentage of alleles fix. Fixation is the process of an allele increasing to a frequency at or near one. The probability of a neutral allele fixing in a population is equal to its frequency. For a new mutant in a diploid population, this frequency is 1/2N.
From: Introduction to Evolutionary Biology
However, see above, a neutral mutation is highly unlikely to spread. My point though is that because you essentially would need all 5 mutations in this case, and the 3rd or 4th would kill the individual, you would never get to the 5th. Think about it. -me- But it doesn't happen that way. There is no planing ahead - if a mutation is detrimental, that's it. So all "modifications" have to work at least as good as the status quo.
I am not talking about planning. What I am talking about is a series of mutations. Not only all modifications have to work as well as the status quo, but none of the mutations in the series can be killing mutations. Otherwise the mutation will be lost. If you go around changing a gene DNA base pair by DNA base pair to try to get an advantageous mutation which perhaps might take five such changes, if any of the other four base changes necessary to achieve that are deleterious the original neutral mutation(s) will be completely lost and you will never get to the 5th one. So the 'additive' method will not work in numerous cases either. Also note that the mutation would also be lost by making incorrect attempts at getting a favorable mutation because the organism carrying it would die and the mutation would be gone with it.