The chance that a string will be copied is based on the string's fitness value , calculated from a fitness function . For each generation, the reproduction operator chooses strings that are placed into a mating pool , which is used as the basis for creating the next generation. There are many different types of reproduction operators . One always selects the fittest and discards the worst, statistically selecting the rest of the mating pool from the remainder of the population. There are hundreds of variants of this scheme.
None are right or wrong.
In fact, some will perform better than others depending on the problem domain being explored. For the moment, we shall look at the most commonly used reproduction method in GAs. To look abstractly at this method, consider the roulette wheel below, which is based on the previous example above. When selecting the three strings that will be placed in the mating pool, the roulette wheel is spun three times, with the results indicating the string to be placed in the pool. It is obvious from the above wheel that there's a good chance that string 10000 will be selected more than once.