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One examined the relative expression (transcription) levels of Y gene between two species of fruit fly: Drosophila melanogaster (" mel ") and D....
One examined the relative expression (transcription) levels of Y gene between two species of fruit fly: Drosophila melanogaster ("mel") and D. simulans ("sim"). The expression level of Y, measured by its mRNA concentration, in the body of mel was observed to be 10-fold higher than the level of Y gene expression in the body of sim. To explain this observation two hypotheses were proposed:
Hypothesis A: A trans-acting factor (= regulatory protein) for Y gene expression in mel is different from that in sim. Namely, mel's trans-acting factor causes more strong transcription activation of Y than sim's trans-acting factor. However, cis-acting factors (= regulatory sequences) of Y genes are identical between mel and sim.
Hypothesis B: A cis-acting factor for Y gene expression in mel is different from that in sim. Namely, mel's cis-acting factor causes more strong transcription activation of Y than sim's cis-acting factor. However, trans-acting factors (= regulatory proteins or transcription factors) of Y genes are identical between mel and sim.
To distinguish between these two hypotheses, additional experiment was conducted: First, F1 hybrid individuals were obtained from a cross between mel and sim flies. Then, in the body of these hybrid flies, the expression level of the mel copy of gene Y was observed to be 10-fold higher than that of the sim copy of gene Y. (mRNA transcribed from mel Y gene can be distinguished from that from sim Y gene due to base sequence differences). Which of the above hypotheses (A or B) is in agreement with this result? Explain with simple diagram.
