Gene flow is :
| 1. | the emergence of new species from pre-existing species | 
| 2. | the exchange of genes during fertilization | 
| 3. | mating between close relatives | 
| 4. | the movement of genes between species populations | 
Genetic drift is :
| 1. | random changes in gene frequency in a population | 
| 2. | generational fluctuations in gene frequencies that produce no effect | 
| 3. | changes due to interbreeding with other species populations | 
| 4. | the effect of mutations as they spread through neighbouring populations | 
The type of natural selection that operates to eliminate intermediate phenotypes in a population is known as:
| 1. | Directional selection | 2. | Disruptive selection | 
| 3. | Stabilizing selection | 4. | Reverse selection |