Tickleback evolution lab final quiz 1. how did some ancestral sea-run stickleback populations come to live exclusively in fresh water? these populations swam to freshwater lakes to spawn and then never returned to the ocean because there were fewer predators in lakes. they became trapped in lakes that formed at the end of the last ice age. they don't actually live exclusively in fresh water; they only live in fresh water at certain stages in their lives. they developed traits that made them better adapted to fresh water and, as a result, had to move to a freshwater environment to survive.

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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.

that scientist would be robert hooke