Final answer:
The selection coefficient for a genotype (aa) when 99 of every 100 organisms successfully reproduce is 0.99.
Step-by-step explanation:
The selection coefficient for a genotype (aa) can be calculated using the formula:
s = 1 - (number of organisms with genotype aa / total number of organisms)
In this case, if 99 out of every 100 organisms successfully reproduce, then the remaining organism does not reproduce. So the selection coefficient can be calculated as:
s = 1 - (1 / 100) = 0.99
Therefore, the selection coefficient for the genotype (aa) is 0.99.