Answer Happy

B) Positive selection
Your laboratory is interested in the gene Paxó, a transcription factor that is essential for the proper development of many tissues including the eye, brain, and pancreas. One hypothesis for how Pax6 expression is made tissue-specific is through several specific enhancer regions that act on the Pax6 promoter in different tissues. You have identified a 341 bp region of genomic DNA (shown in purple below) that you believe is an enhancer region that specifically drives the expression of Pax6 in the eye but not in other tissues. You are interested in knocking out this region of DNA. Shown below is a schematic of the wild type allele of the gene carrying the putative enhancer element, and a targeting vector (construct) designed for making a knockout mouse. Wildtype allele Targeting vector So 8kb K (Sa) RN 1.7kb 10kb 469 3.8kb DA neo KH 4kb (A) Sp PA Key: Pr - promoter: pA = poly A tail Notes: Information about restriction sites (labeled R. N. K.A. Sa, or Sp) or the genomic distances indicated in kb are not needed for answering this question. Identify the elements on the targeting vector (construct) that confer the following aspects and provide an explanation for how they work: