MIT Department of Biology 7.013: Introductory Biology - Spring 2005 Instructors: Professor Hazel Sive, Professor Tyler Jacks, Dr. Claudette Gardel Cancer Pedigrees Section Answers Individual A has been diagnosed with familial adenomatous polyposis - a type of colon cancer. Investigation of the individual's family history yields the following pedigree for colon cancer (where the shaded individuals have colon cancer). Assume people marrying into this family carry 2 wildtype alleles. A a) Based on the pedigree, what is the mode of inheritance? (X-linked recessive, X-linked dominant, autosomal dominant, autosomal recessive)? How do you know? Every generation, A has the disease and can only get good copies from DAD so 1 bad copy from Mom is enough to get the disease. Actually from the pedigree alone, X-linked recessive could be a possibility as well! The later PCR analysis on the next page rules out this possibility. In order to isolate the disease gene responsible for this type of colon cancer, you look for markers linked to the disease phenotype. You score each family member for the presence of a marker with 4 alleles: 1, 2, 3, and 4. The results are listed below. b) Which marker(s), if any, are linked to the colon cancer phenotype? Briefly explain. Marker #2 is linked to the diseaase phenotype. All affected individuals in this family have marker #2. No one without thie disease has marker 2.Cancer Pedigrees continued One year later you identify the disease gene – “adneomatous polyposis coli” or APC- and you perform an analysis to find the mutations causing colon cancer in this affected family. Using PCR followed by sequencing techniques, a nonsense mutation in the APCgene of Individual A is found. This mutation creates an HpaI restriction site in the gene. Using PCR, you amplify the APCDNA fragment from various tissue samples and perform RFLP analysis with the restriction enzyme HpaI. These digests are run out on an agarose gel shown below. aa Aa Aa Aa Aa c) In the spaces provided above, fill in the APCgenotype for each tissue. (Use A to define the wild-type allele.) d) How do you account for the results in part c? Affected individuals in this family have inherited one mutant copy of APC. In tumor tissue, they have last the remaining WT copy. This loss of both copies leads to cancer or the tumor. e) At the cellular level, is the cancer phenotype of the mutant APCgene... dominant or recessiveCircle one. In order to study the colon cancer further, you propose making a mouse model for the human disease. The first step is to identify the mouse gene. f) Given the human APCgene and an agarose gel of sized cut mouse genomic DNA, name the technique or process that would allow you to determine if there’s a mouse gene similar to the human APCgene. ___________Southern, hybridization, Watson and Crick pairing, probing, etc._g) Given you find the mouse gene and are able to create a deletion within it, how could you create a transgenic mouse where some of its cells will have this deletion? Can grow ES cells in culture, can insert your deleted copy into ES cells by homologous exchange, can put these cells into early mouse embryo --> striped
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