Question 1
Paper 1A style
HL only (what this means)
HL only: additional Higher Level content, only for HL students. SL students can skip it. What the labels meanWhich statement correctly compares a liver cell and a skin cell from the same person?
- They have different genomes and the same proteome
- They have the same genome and different transcriptomes
- They have the same transcriptome and different proteomes
- They have different genomes and different transcriptomes
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Answer: B
Question 2
Paper 1A style
HL only (what this means)
HL only: additional Higher Level content, only for HL students. SL students can skip it. What the labels meanWhat is the effect of methylation of cytosine bases in the promoter of a gene?
- The base sequence of the gene is changed
- Transcription of the gene is repressed
- Translation of the mRNA is increased
- The mRNA is broken down more quickly by nucleases
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Answer: B
Question 3
Paper 2A style
HL only (what this means)
HL only: additional Higher Level content, only for HL students. SL students can skip it. What the labels meanOutline two ways in which a cell can regulate the amount of a protein it produces.
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- transcription factors bind to specific base sequences in DNA [1]
- at the promoter, where RNA polymerase binds [1]
- activators binding to enhancers increase transcription / repressors decrease it [1]
- control of the rate of mRNA degradation (by nucleases) [1]
- mRNA may persist for minutes up to days [1]
- longer-lasting mRNA can be translated more times, so more protein is made [1]
- max 4
Question 4
Paper 1B style
HL only (what this means)
HL only: additional Higher Level content, only for HL students. SL students can skip it. What the labels meanResearchers measured differences in DNA methylation between the two members of pairs of monozygotic twins. A higher score means the twins' methylation patterns are more different (the data are for practice). (a) Describe the trend shown by the data. [1] (b) Explain why monozygotic twins are used to investigate the effect of the environment on gene expression. [2] (c) Suggest why twins who had lived apart for longer showed larger differences. [1]
| Age of twins / years | Mean difference in methylation | Mean years lived apart |
|---|---|---|
| 3 | 0.8 | 0 |
| 18 | 1.9 | 1 |
| 35 | 3.4 | 14 |
| 50 | 4.6 | 27 |
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- (a) difference in methylation increases with age (and years lived apart) [1]
- (b) monozygotic twins have identical genomes / same base sequences [1]
- so differences in methylation / gene expression must be caused by the environment [1]
- (c) more time in different environments / diets / exposures to pollutants alters methyl tags differently [1]
Question 5
Paper 2A style
HL only (what this means)
HL only: additional Higher Level content, only for HL students. SL students can skip it. What the labels meanExplain how the presence of lactose changes gene expression in E. coli.
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- without lactose, a repressor protein binds to the operator (of the lac operon) [1]
- this blocks RNA polymerase so the genes are not transcribed [1]
- lactose / allolactose binds to the repressor, changing its shape [1]
- repressor detaches from the operator, so RNA polymerase transcribes the genes [1]
- enzymes for uptake / breakdown of lactose / β-galactosidase are produced [1]
- max 3
Question 6
Paper 2B style
HL only (what this means)
HL only: additional Higher Level content, only for HL students. SL students can skip it. What the labels meanExplain how epigenetic tags can affect the phenotype of cells and offspring without changing the genotype. Refer to tigons and ligers in your answer.
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- epigenetic tags do not change the base sequence of DNA, so the genotype is unchanged [1]
- methylation of cytosine in a promoter represses transcription [1]
- methylation of histones can repress or activate transcription [1]
- changes the pattern of gene expression / which proteins are made, so changes the phenotype [1]
- patterns of tags lead to differentiation / epigenesis [1]
- tags can remain in place during mitosis / be passed to daughter cells [1]
- most but not all tags are removed from the ovum and sperm [1]
- so some tags pass to offspring / effect depends on which parent an allele came from (imprinting) [1]
- liger (male lion × tigress) is larger than tigon (male tiger × lioness) though both have lion and tiger genes [1]
- strong paternal growth-promoting imprinting from the lion father is not balanced by the weaker maternal growth-restraining imprinting of a tigress OWTTE [1]
- tigon: strong maternal growth restraint from the lioness and weak paternal growth promotion from the tiger, so not enlarged [1]
- max 6