| Date | May 2017 | Marks available | 1 | Reference code | 17M.3.HL.TZ1.9 |
| Level | Higher level | Paper | Paper 3 | Time zone | Time zone 1 |
| Command term | Explain | Question number | 9 | Adapted from | N/A |
Question
The cladogram is based on a comparison of open reading frames in DNA taken from fungi. It is an example of how open reading frames can be used in phylogenetic studies.
Outline how open reading frames are identified in DNA.
Explain what the branching off points represent in the cladogram of these fungi.
There are several methods of introducing DNA into a cell in the laboratory. Outline the introduction of recombinant DNA in plant cell protoplasts.
Markscheme
a. identify a start codon and stop codon
b. identify base sequences for a gene/that could code for a polypeptide
c. possible correlation with existing open reading frames in databases
a. represent common ancestors shared by the organisms that emanate from the point
b. indicates time since divergence
c. indicates number of differences in DNA
a. plant cells made into protoplasts by removing their cell wall / use cellulase to produce protoplasts
b. physical methods such as electroporation /microinjection/biolistics
c. chemical methods such as liposomes/calcium chloride/polyethylene glycol «PEG»
d. vectors such as Agrobacterium/tobacco mosaic virus
Examiners report
Syllabus sections
- 17M.3.SL.TZ1.16a: Calculate the diversity of site C. Working should be shown.
- 18M.3.HL.TZ2.12b: Regulations say that a protein is considered allergenic and unsafe for human consumption if...
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18M.3.HL.TZ1.12a:
Caenorhabditis elegans, a nematode, was the first multicellular organism whose genome was completely sequenced.
Outline the benefits of using model organisms for studying gene function.
- 18N.3.HL.TZ0.11d: A bioinformatics analysis was performed on the protein PSY transcribed from the gene from...
- 16N.3.HL.TZ0.12e: Determine which two genera are most closely related according to their cytochrome c protein...
- 17N.3.HL.TZ0.10a: Identify the species that has the lowest percentage of coding sequences.
- 17N.3.HL.TZ0.10b: State how similar nucleotide sequences can be identified.
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16N.3.HL.TZ0.12c:
(i) Identify the longest amino acid sequence where there are no differences amongst the five genera.
(ii) Suggest, with a reason, whether the DNA coding for the amino acid sequence identified in (c)(i) must be identical for the five genera.
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16N.3.HL.TZ0.12b:
State the meaning of the dash (–) in the alignment.
- 18N.3.SL.TZ0.10d: Describe how bioinformatics can help identify genes within the DNA of an organism.
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18M.3.HL.TZ1.12b:
Describe how BLAST can be used to establish phylogenetic relationships between several organisms.
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18N.3.HL.TZ0.11f:
In the alignment there are dashes (–) in some positions. Deduce what is indicated by these dashes.
- 18N.3.HL.TZ0.11e: BLASTp was used to obtain the alignment of the genes coding for PSY. Outline reasons for...
- 18M.3.HL.TZ2.12a.ii: Outline how the similar protein sequences were found.
- 17M.2.HL.TZ1.1f.ii: Suggest a reason for the greater expression of the gene for the urea transporter after an...
- 16N.3.HL.TZ0.12a: State the bioinformatics tool used to obtain the alignment.
- 16N.3.HL.TZ0.12d: Describe briefly how the cladogram was obtained.
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17M.3.HL.TZ1.12:
Explain how BLAST searches are carried out and the applications of different types of these searches.
- 18M.3.HL.TZ2.12a.i: State a bioinformatic search tool that could be used to perform the alignment.
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17N.3.HL.TZ0.10c:
The yeast Saccharomyces cerevisiae was the first eukaryotic organism to have its entire genome sequenced. Suggest reasons for the choice of yeast as a study organism.
