Response To Questions From Part A To B A. A precancerous condition (intestinal p

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Response To Questions From Part A To B A. A precancerous condition (intestinal polyposis) in a particular human family is determined by a single dominant gene Among the descendants of one woman who died with cancer of the colon, 10 people have died with the same type of cancer and 6 now have intestinal polyposis. All other branches of the large kindred have been carefully examined, and no cases have been found. In whom did the defective gene originate? In what cells? Be specific and explain vour reasonin Charles YanOfSk studied the tryptophan synthetase gene of E. coli in an attempt to identify the base sequence specifying this protein. The wild type organism had a protein with a glycine in position 38. Yanofsky isolated two trp mutants: A23 and A46. Mutant A23 had Arg instead of Gly at position 38, and mutant A46 had Glu at position 38 Mutant A23 was plated on minimal medium and four spontaneous revertants to wild type were obtained. For each of these revertants, the amino acids at position 38 were determined and are shown in the figure below. Revertant 1 had Ile, revertant 2 had Thr, revertant 3 had ser, and revertant 4 had gly. In a similar fashion, three revertants from A46 were isolated and the amino acids at position 38 were determined and are shownbelow B. a) Using the genetic code, deduce the codons for wild type, the mutants, and the revertants, and write them in the space provided in the figure. These are all single base pair mutations b) Discuss why 5 of the 7 revertants still functioned as a wild tvpe organism, even though the amino acid at position 38 did not change back to Gly! Gly Wild Type Arg Mutants le Thr Ser Gly Gly Val Revertants

Explanation / Answer

Ans. A) The defective gene was originated in the descendants of the lady who died with the cancer of colon. The single defective dominant gene occurs due to the mutation in APC (adenomatous polyposis coli) gene

-These occurs in the epithelium of large intenstine.or on the lining of colon.

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