Base analogs can be used in the sequencing of DNA. Certain base analogs can be added to the growing DNA chain, but due to the lack of a hydroxyl group, no further bases can be added. That stops the growing chain. If a piece of DNA is replicated in a solution containing some of those base analogs, chains will be made that end after whatever analog has been added is used.
When the above experiment is run using analogs for all four bases (separately) and then are run on a gel, the DNA sequence can be read off. Every time a base analog was added, it will terminate the chain, and there will be DNA pieces of that length. That way every different length of DNA strand will be formed, and which lane any given piece is in is determined by what base analog was used to terminate the chain of that length, and thus what base is in that position.
The digital time base error signals are evaluated at sampling instants which correspond to the rhythm of the line synchronizing pulses, for which purpose the line synchronizing pulses applied to the input 30 of the detector circuit 29 are also applied to a further input 39 of the converter 37.
Quantization of the amplitudes of the analog time base error signal for the formation of the time base error signals at the individual sampling instants is effected in units which correspond to a given time interval, which results in a corresponding number of bits.
Thus, the control range for the correction of time base errors as regards the maximum magnitude is governed by the capacity in respect of the number of addresses of the memory 8, and as regards the minimum magnitude by the selected clock frequency for writing into the memory.
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