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MCAT Question A Day - 4/19/14 - Answer!

Chromosome puffs can be observed along giant polytene chromosomes in the salivary gland cells of insect larvae. They appear to be regions of DNA that uncoil or decondense. The locations of puffs change at different times during larval development in response to hormonal signals. This phenomenon is an example of

A.  gene regulation at the transcriptional level.
B.  a polygenic trait.
C.  posttranscriptional RNA processing.
D.  gene expression at the translational level.

The correct answer is (A). A basic understanding of the processes of transcription and translation is needed. If chromosome puffs represent uncoiled or decondensed regions of DNA, this suggests that the DNA sequence has to be “read,” either for DNA replication (mitosis) or protein synthesis. Since the insect larva is undergoing different developmental changes in response to hormones, the synthesis of various proteins needed during each subsequent stage seems most probable. The hormone appears to be “activating” genes along the DNA so that transcription of these DNA sequences can occur.

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