Question

question 3 of 10
a population of animals is split in half by a river. before speciation is
completed, the two halves are rejoined when a drought causes the river to run
dry. how would this impact the two populations?
a. gene flow would increase between the two halves, and speciation
would not occur.
b. traits that had developed through mutation would still exist in
only one of the halves.
c. speciation would still occur, because the two halves would be too
different genetically to interbreed.
d. the two halves would be reproductively isolated.

Explanation:

Speciation wasn't completed. When the river dries and the two populations are rejoined, gene flow can occur. But traits that developed via mutation in one isolated - half (during the separation) would remain only in that half initially. Gene flow (A is wrong as gene flow would occur). Speciation didn't complete, so they aren't too genetically different to interbreed (C is wrong). Since the river dried, they are no longer reproductively isolated (D is wrong).

Answer:

B. Traits that had developed through mutation would still exist in only one of the halves.