Answer:
The correct answer would be - Genetic drift within the small populations in the test tubes resulted in different genotype frequencies
Step-by-step explanation:
Genetic drift is not like natural selection or adaptive radiation as it is a phenomenon that is random and does not takes place on the basis of genes being beneficial or harmful for survival. Genetic drift depends on any kind of error when the shift occurs in successive generations. Genetic drift also altered the allele frequency of a particular characteristic in future generations.
In this experiment, the sample cultures are transfer from one test tube to another on daily basis for a time period of two months There must be some sampling error that occured and caused the change in allelic frequency as natural selection cannot undergo under such a small population or within such short life span or time period only genetic drift can cause it.