Q28 - Southern Blot Evidence for Immunoglobulin Light-Chain Gene Rearrangement

Theoretical 1 Real exam question - full text reproduced under IBO's CC BY-NC-SA 4.0 license

Recombinant DNA & Biotechnology Techniques Gene Regulation: Eukaryotic & Epigenetics

Immature lymphocyte B cells differentiate in an area of the peripheral lymph organ called the embryo center. Myeloma cells are tumor cells that produce one type of mature immunoglobulin. mRNAs for full-length or only 3’ half of the immunoglobulin light chain gene were purified from a myeloma cell and were radioisotope-labeled. Genomic DNA fragments obtained from either the embryo center or myeloma cells were digested with a restriction enzyme and size fractionated by agarose electrophoresis. These DNA were hybridized with radiolabeled mRNA, and radiation was measured after the removal of unhybridized mRNA (the experimental flow is shown in Figure 1). The results are shown in Figure 2. Indicate whether the sentences below are correct or incorrect.

Figure 1. Figure 1.

Figure 2. Figure 2.

Using the information and data, determine which of the statements are true or which are false.

A. The immunoglobulin light chain gene contained in the embryo center cells is shorter than that in the myeloma cells.

B. The running distance depends on the length of DNA hybridized with mRNA.

C. The nucleotide sequence of DNA region hybridized with 3'-end mRNA is different between the myeloma-derived DNA and the embryo center-derived DNA.

D. The full-length immunoglobulin light chain mRNA isolated from myeloma cells contains sequences from two different parts of the DNA genome of the embryo center cells.

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Question reproduced from IBO 2020, Theoretical Exam 1, licensed under CC BY-NC-SA 4.0 - attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)