Hw2
- 1. HW#2 Genetics 320, Fall 07. Due Wed, Sept 12 The rules for this homework are the same: type any answers that involve words, except if you are filling in a table then write CLEARLY, or it will be marked wrong. If you don’t know what CLEARLY means, type your answers in the table. I give you a lot more problems this week than last. Many questions are revised from previous exam questions, to give you an idea what exam questions might look like.
- 2. Page 1 Another gene expression, mutation and consequences. The DNA sequence of the top strand is shown. Capital letters indicate consensus promoter sequence (TATA) or coding sequence (ATG…TAG). The expression of the protein requires p53. The function of the protein requires all the specific amino acids in the ORF shown. +1 of the mRNA is a C. There is no splicing. The ATG (at +5,6,7) is the start codon. Answer the following questions (with the help of the Genetic Code given below). p53 binding site gcgTATAccgctacgtagg c tttATGCGATTTAAACCCTAGcccgcaag +1 +5 Transcribed? Translated (#amino acids) Functional? a. p53+/+ YES YES (full length) YES b. TATAcc to TggAcc c. Delete c at +1 d. Insert T between 7G &8C e. Delete ccc after TAG f. AAA to AAG Enter YES or NO. 1pt each. Enter # of amino acids if different from wildtype gene. You can explain ambiguities on the other side of this sheet (you shouldn’t need to!) g. Explain briefly your answer to c and 2d.
- 3. Page 2 2. Recombination Refer to the chromosomes of a G2 cell shown below. -label two sisters with “S” -label two homologs with “H” b. Draw the recombination and segregation events to form an A+a- B+b- cell. b- a- B+ A+ c. Harder question : This AaBb mitotic cell (diagram) could generate either aaBb, Aabb, and aabb cells. Which of these three would be formed least frequently and why? In a Mitotic cell-a-c . In a Meiotic cell d. d. Draw a double Holliday structure intermediate from strand invasion step before replication occurs. NEATLY! - Draw an arrow to the D loop . Indicate the polarity of all 4 strands in your diagram. - Circle each 3’ site where DNA polymerase synthesizes DNA, and place dots what it synthesizes. - Place a square around ONE Holliday structure and a triangle around one site of potential heteroduplex (without further branch migration) -Place slashs showing one way this could be resolved to form a crossover.
- 4. Page 3 3. True/False, short, relevant answer to all questions. RNA polymerase stops transcription when it comes to a stop codon. b. Bases at the 5’ end (upstream) of the start codon set the reading frame for the ribosome. The “Protein Interaction Network” is a bunch of worthless hooee. Spo11 and RecA cut DNA to make a doublestrand break to start mitotic recombination. In a hypothetical population of bees, the p53+/- diploids and p53+/-/- triploids get cancer at about the same frequency. The Philadelphia chromosome is an example how a base pair change by DNA polymerase leads to a drastic genetic change. Drugs that target a specific domain are unlikely to specifically interact with the protein that are designed to interact with.
- 5. 4. Consider the cell 1 and cell 2 with the chromosomes shown. In Cell 1, Gene A is 50cM from the centromere, and in Cell 2 Gene C is 10cM from the centromere. In both cells the wildtype allele is on the top homolog, and the mutant allele on the bottom homolog. This problem involves mitotic recombination . Gene A+ + - a. Will Cell 1 or Cell2 form homozyous mutants at the highest frequency? Explain. b. A new Cell 3 is like Cell 1 except that it has a recessive lethal mutation. d- 10cM to the left of the GeneA+ allele. Where would the D+ allele be in Cell 3? (this should be obvious) c. Will Cell 1 or Cell 3 give the most viable a-/a- mutants? Explain. Cell 1 Cell 2 Gene C + -
- 6. 5 . The mutational spectrum found in cancer cells of the p97 protein and its domains is shown. (There are 4 “hotspots” in the DNA binding domain.) p97 mutant cells get cancer at a high rate. Amino Acid# 1 150 250 350 390 450 545 Transcriptional Activation DNA binding Trimerization domain What does “hot spot” mean in this diagram? The few mutations in the rectangle and circle domains were usually nonsense or frameshift mutations. Why might these mutations lead to mutant p97 while missense mutations in these domains do not typically lead to mutant p97? C. Would would the molecular consequence and phenotype be of a nonsense mutation in codon 5? Frequency Of mutations
- 7. 6. Explain why a person with a germline genotype of p53+/- is prone to cancer while a person with a germline genotype of CFRT-/+ is not prone to cystic fibrosis. 7. In the pedigree shown below, compare the relative extent of heterology (between any two homologous chromosome) in individual 1, individual 2 and individual 3. 1 2 3
- 8. 8. Below are two genes that are present in a diploid cell on different chromosomes. Rare translocations occur between Gene A site 1 and Gene B site 3, or between GeneA site 2 and Gene B site 3. Site 1, 2 and 3 are all in exons. The recombination occurs within runs of polyA at each site. The length of As is show. One example of a site 1-site3 translocation is shown. Gene A is normally induced by DNA damage. Will the GeneA-GeneB fusion gene show in the diagram now be induced by DNA damage? Only 1 in 3 translocations between Site 1 and Site 3 leads to an active GeneB protein fusion. Explain. c. The black exon in Gene B has Gene B’s main function. Would you expect recombinaton between introns I-A and I-B to necessarily generate an active B protein fusion? Discuss . I-A I-B TATA Box TATA Box A30 +1 p53 site A50 A5 +1 p53 site A TATA Box +1 40 Site 1 Site 2 Site 3 GeneA GeneB GeneA-B