BIOL UN2005 Midterm: Exam 4 2017

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turquoisegnu128

31 Jan 2019

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Most questions and explanations are 2 pts each. Key to exam #4 dec 19, 2017 -- corrected 12/28/17: look at the pedigree on the info page. All the affected people in this pedigree have the same rare condition (call it nb night blindness) and the same mutation. I:1 and i:2 do not carry this mutation. The mutation is in a gene on the x chromosome. Note that in generation two, there are 10 unaffected individuals (whose sex is not specified), and one male with nb. The numbers below refer to the numbers given in the pedigree: if the whole family tree were written out, including all the individuals in generation ii, the affected individual in generation ii would be labeled______ii-11___. (no explanation required. We want numbers, not genotype. : the mutation causing nb in this family, probably occurred during meiosis in (ancestor of i:1) (ancestor of i:2) (i:1 or i:2) (i:1) (i:2) (ii:1) (ii:2) (beats me).

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In the October 2011 issue of PLoS Genetics, Pierson et al. used whole-exome sequencing to identify the mutations responsible for a rare spastic ataxia-neuropathy syndrome. The paper and supporting information can be found at http://journals.plos.org/plosgenetics/article?id=10.1371/journal.pgen.1002325, and you will need to access the paper to answer these questions. The paper is focused primarily on the phenotype and the particular gene, but our attention will be primarily on the methods used for the exome-sequencing approach, which is found in the Methods and in the Supporting Information.

a. Figure 1A shows a pedigree of the family with two affected sons, who are not identical twins.

i. Recalling pedigree analysis from your introductory genetics course, what is the most likely mode of inheritance for this syndrome?

ii. What is the probability that the next child born to this couple will be disease-free?

b. Summarize the experimental strategy that yielded the results shown in Supplemental Table S2, as found under Supporting Information. Your summary should define the abbreviations used in the column headings and what the numbers mean. You should also include an explanation of why the numbers decrease as one reads from left to right from columns 2 through 6 (not including Total Protein Coding Exons Sequenced). c. The numbers of candidate genes in Supplemental Table S3 are 71 and 7, but these numbers do not appear anywhere in Supplemental Table S2. What inference from the data was made that allowed the investigators to arrive at the numbers in Table S3 based on the numbers in Table S2?

d. What further inferences led the investigators to conclude that AFG3L2 is the gene most likely responsible for this syndrome?

e. In the analysis of Miller Syndrome described in the chapter, the affected children did not have the same mutation on each homologous chromosome, and were in fact heteroallelic for the mutations. In this example, the children have the same mutation on each homologous chromosome. Why did the authors expect that the affected children would be homozygous for the same mutation?

f. What is the postulated mechanism by which this mutation results in this phenotype?

g. In this chapter, genes can be cloned and identified based on the following five properties: map position, mutations and allelic differences, expression patterns, complementation testing, and homology with genes in other organisms. Using a flow chart, diagram how these five properties led to the identification of the gene for this syndrome.

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BIOL UN2005 Midterm: Exam 4 2017

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