The animations I've seen that purport to show the general public how DNA replication works indicate that it is a sequential process. The DNA is split into two strands, kind of like a zipper unzipping, and then bases are added to the two strands to form the two new complete DNA molecules. One strand (the leading strand) has the new bases added one after the other in the same direction. The other strand (the lagging strand) has them added in short called Okazaki fragments.
Errors on the leading strand should be independent and occur at a constant rate, and so having useless zones should have no effect on the number of errors a given useful zone gets.
The lagging strand is more complicated, because you have at least 3 distinct things going on: finding where to start on Okazaki fragment, filling it in, and recognizing the end. I suppose that allows for a different kind of error on the lagging strand (messing up recognizing the start or end of an Okazaki fragment) that would affect multiple consecutive base pairs. Useless segments would increase the average spacing between useful segments, and so would decrease the chance that a given multi-base error in a useful fragment affects multiple segments.
However, the problem here is that the enzymes aren't perfect and coding errors are quite common (they get fixed, sometimes). A big problem is that some chemicals can look like a nucleotide (A or T or C or G) and after insertion it can "decay" into a different one, hence causing an error. During replication it is possible for a DNA fragment to be cleaved (once again, it is often repaired, but thats how the Y chromosome came to be AFAIK) however sometimes enzymes "mess up" and reattach them at wrong positions. At other times base-pairs are deleted or inserted shifting the whole strand. There is a lot of things that could go wrong.
The animations I've seen that purport to show the general public how DNA replication works indicate that it is a sequential process. The DNA is split into two strands, kind of like a zipper unzipping, and then bases are added to the two strands to form the two new complete DNA molecules. One strand (the leading strand) has the new bases added one after the other in the same direction. The other strand (the lagging strand) has them added in short called Okazaki fragments.
Errors on the leading strand should be independent and occur at a constant rate, and so having useless zones should have no effect on the number of errors a given useful zone gets.
The lagging strand is more complicated, because you have at least 3 distinct things going on: finding where to start on Okazaki fragment, filling it in, and recognizing the end. I suppose that allows for a different kind of error on the lagging strand (messing up recognizing the start or end of an Okazaki fragment) that would affect multiple consecutive base pairs. Useless segments would increase the average spacing between useful segments, and so would decrease the chance that a given multi-base error in a useful fragment affects multiple segments.