Genetics 371B Practice problems--Autumn 2000 week 5
Answer key is here
Mainly Lectures 13-15
| 1. | The DNA sequence flanking a certain polymorphic microsatellite repeat site is shown:
|
|
| (a) |
Which of the following primers would you use to amplify the repeat site (in its entirety) by PCR? (How many primers are needed?) (i) 5'-CATCCTAGGGCTTATC-3' (ii) 5'-GCGGATAAGCCCTAGG-3' (iii) 5'-CACACACACACACACA-3' (iv) 5'-CAGCCATATCAGCAAT-3' (v) 5'-TCTGATTGCTGATATG-3' |
|
| (b) | The genotype of an individual with respect to this polymorphic site is [3,7]. Explain what this notation means, writing out the sequence of the same portion of the chromosome as shown above. | |
| 2. | An orphan strikes it rich playing Powerball. Within days, three burly men show up, each claiming to be her long-lost but devoted father. As the resident geneticist, you obtain DNA samples from all four people involved and look at their profile for three different polymorphic microsatellite repeat loci. The results from the tests (PCR products separated by gel electrophoresis) are shown:
Based on these results, and on the allele frequencies shown above -- |
|||||||
| (a) | Can you conclusively eliminate one or more of the candidate fathers? If so, which one(s), and why? | |||||||
| (b) | Which of the candidates are you more inlined to believe, and why? Is this a firm conclusion? | |||||||
| (c) | Based on your answer in (b), construct a partial profile of the young woman's mother for each of the three loci. | |||||||
| 3. | The plot below shows linkage analysis of two human disease genes with respect to a three polymorphic loci. Each curve represents the distribution of lod score vs. recombination frequency for one of the polymorphic sites with respect to one of the disease genes.
|
|
| (a) | Construct a linkage map that best fits the data shown. (Note: Pairs of data sets -- e.g., 'a' and 'e' -- are shown here as overlapping perfectly. You wouldn't normally expect to find this kind of perfect overlap.) | |
| (b) | Can you state what assumption is being made when you infer a precise map location based on the apex of each curve? If you were trying to map a gene for positional cloning, would you feel comfortable with that assumption? | |
| 4. | You heard in lecture about reversal of the Niemann-Pick C phenotype by introduction of the wildtype gene into cultured Niemann-Pick cells. Now refer back to the pedigree shown in Week 2, Practice Question 5. Suppose this disease also caused a phenotype that could be detected readily in cultured cells derived from patients with the disease. Would introduction of the wildtype gene in this case reverse the disease phenotype in these cultured cells? Why, or why not? | |
| 5. | For each of the following mutations, say whether you expect the mutated form of the gene to give a dominant or recessive phenotype, and why (but note that more than one answer may be possible): | |
| (a) | a promoter mutation that eliminates transcription of a gene | |
| (b) | a promoter mutation that causes inappropriate expression of the gene (i.e., it is transcribed even when it shouldn't be, or in a location or cell type where it shouldn't be) | |
| (c) | a frameshift mutation near the beginning of the gene that results in a truncated protein | |
| 6. | You heard in lecture that H. J. Muller used a balancer chromosome to prevent crossing over in the X chromosome in his experiment to estimate the frequency of spontaneous mutations in Drosophila. Why was it so important to prevent crossovers? | |
| 7. | Ted Weinert and Lee Hartwell discovered that rad9-defective yeast cells are viable as long as their DNA is not damaged, but die within one or two cell divisions if their DNA is damaged, presumably because they fail to arrest the cell cycle in response to DNA damage. One observation these researchers made was that if they treated the rad9-defective cells with the drug nocodazole for a few hours immediately after administering the DNA damage, the cells would no longer die. Nocodazole is a drug that blocks the formation of microtubules. | |
| (a) | What effect do you think nocodazole has on the cell cycle? (Where have you heard about microtubules before?) | |
| (b) | Suggest an explanation for the rescue of viability by treatment with nocodazole. | |
| 8. | A bacterial geneticist is working with two strains of bacteria that are genetically identical except for one location in the chromosome ("Site B")-- whereas strain #1 has the sequence 5'-GGATCC-3' at Site B, strain #2 has the sequence 5'-GAATCC-3'. GGATCC happens to be the recognition sequnce for the restriction enzyme BamHI, so the DNA from strain #1 can be cut by BamHI at Site B, while DNA from strain #2 is resistant to BamHI at Site B.
The scientist makes the following observation: if she treats strain #1 with a mutagen, about 1 out of every million mutagenized cells becomes resistant to BamHI at site B. When she treats strain #2 with the mutagen, she finds that now some cells have become sensitive to cutting by BamHI at Site B -- but only about 1 in 24 million cells have become sensitive. Explain why the frequency of the events was so different between the two treatments. |
|
Also do:
