Bird guides once listed the myrtle warbler and Audubon's warbler as distinct species because of differences in color patterns of the feathers and size of the beak. Recently these birds have been reclassified as eastern and western forms of a single species, the yellow-rumped warbler, based on the observation that the two forms interbreed often in nature and the offspring have good survival and reproduction. The earlier classification into two species was using a species concept; the reclassification is using the species concept.

morphological; biological

Explanation:

The morphological species concept highlights the importance of physical traits to delimit species. This concept is useful for classifying asexually-reproducing organisms and where lack information on interbreeding (for example, to classify fossils). On the other hand, the biological species concept states that one species represent a group of organisms that can interbreed (or potentially can interbreed) in order to produce fertile offspring. The biological species concept is nowadays the most widely accepted concept to define species.

the index of refraction of the second medium is higher. i just took the test trust me !

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.