The answer is either A, the bottleneck effect or C, natural selection. The answer is most likely A because it is hinted that the predator fish was placed in the isolated stream. The predators eating the darters less than 5cm is natural selection though.
A: the F1 generation
Parental cross:: WWDD x wwdd
Possible Gametes for each parent: WD& wd
B: The F2 generation
F1 cross WwDd x WwDd
Possible Gammetes for each parent: WD, Wd,wD, or wd
