**Geographic isolation caused the separation of rainforest frog populations into a population in the north and a population in the south. The separated populations later reconnected because the climate got wetter
and warmer, causing the rainforest to expand. When males from the north mated with females from the
south, the offspring failed to develop past the tadpole stage. When males from the south mated with
females from the north, the offspring developed more slowly than the offspring of pairs of northern frogs.
These data support that which event occurred while the two populations of frogs were separated?
a. The two populations developed into new species.
b. The two populations mated with other species of frogs.
C. The two populations began a new method of reproduction.
d. The two populations had fewer offspring than before the separation.

step 1: initiation

initiation is the beginning of transcription. it occurs when the enzyme rna polymerase binds to a region of a gene called the promoter. this signals the dna to unwind so the enzyme can ‘‘read’’ the bases in one of the dna strands. the enzyme is now ready to make a strand of mrna with a complementary sequence of bases.

step 2: elongation

elongation is the addition of nucleotides to the mrna strand. rna polymerase reads the unwound dna strand and builds the mrna molecule, using complementary base pairs. there is a brief time during this process when the newly formed rna is bound to the unwound dna. during this process, an adenine (a) in the dna binds to an uracil (u) in the rna.

step 3: termination

termination is the ending of transcription, and occurs when rna polymerase crosses a stop (termination) sequence in the gene. the mrna strand is complete, and it detaches from dna.