You have developed a strain of transgenic mice that express a human β-globin gene. Your transgenic construct includes all 3 exons of the human β-globin gene plus 500 nucleotides of both 5′- and 3′-flanking sequences. Examination of these transgenic mice shows that the human β-globin construct is expressed at levels about 10-fold lower than the endogenous mouse β-globin gene. Which of the following regulatory elements is most likely missing from your transgenic construct, thereby explaining the reduced level of expression?
A) enhancer elements
B) mRNA splicing signals
C) polyadenylation signals
D) promoter elements
E) silencer elements

Question

Quizplus · Accepted Answer

Enhancer elements are regulatory DNA sequences that, when bound by specific proteins, can significantly increase the transcription of a gene. The absence of these elements in the transgenic construct could lead to lower expression levels of the human β-globin gene compared to the endogenous mouse gene.  Enhancer elements are cis-acting- DNA sequences that can increase transcription of genes. Enhancers can usually function in either orientation and at various distances from a promoter. The β-globin construct used to create the transgenic mice most likely did not include the appropriate enhancer element(s) that are present in the endogenous mouse β-globin gene, thereby accounting for the reduced expression of the transgene.

You Have Developed a Strain of Transgenic Mice That Express