SL Content Statements

• D1.3.1

  Gene mutations as structural changes to genes at the molecular level

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  Distinguish between substitutions, insertions and deletions.
  

• D1.3.2

  Consequences of base substitutions

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  Students should understand that single-nucleotide polymorphisms (SNPs) are the result of base substitution mutations and that because of the degeneracy of the genetic code they may or may not change a single amino acid in a polypeptide.
  

• D1.3.3

  Consequences of insertions and deletions

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  Include the likelihood of polypeptides ceasing to function, either through frameshift changes or through major insertions or deletions. Specific examples are not required.
  

• D1.3.4

  Causes of gene mutation

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  Students should understand that gene mutation can be caused by mutagens and by errors in DNA replication or repair. Include examples of chemical mutagens and mutagenic forms of radiation.
  

• D1.3.5

  Randomness in mutation
  

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  Students should understand that mutations can occur anywhere in the base sequences of a genome, although some bases have a higher probability of mutating than others. They should also understand that no natural mechanism is known for making a deliberate change to a particular base with the purpose of changing a trait.
  

• D1.3.6

  Consequences of mutation in germ cells and somatic cells
  

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  Include inheritance of mutated genes in germ cells and cancer in somatic cells.
  

• D1.3.7

  Mutation as a source of genetic variation
  

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  Students should appreciate that gene mutation is the original source of all genetic variation. Although most mutations are either harmful or neutral for an individual organism, in a species they are in the long term essential for evolution by natural selection.
  NOS: Commercial genetic tests can yield information about potential future health and disease risk. One possible impact is that, without expert interpretation, this information could be problematic.
  

AHL Content Statements

• D1.3.8

  Gene knockout as a technique for investigating the function of a gene by changing it to make it inoperative
  

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  Students are not required to know details of techniques. Students should appreciate that a library of knockout organisms is available for some species used as models in research.
  

• D1.3.9

  Use of the CRISPR sequences and the enzyme Cas9 in gene editing

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  Students are not required to know the role of the CRISPR–Cas system in prokaryotes. However, students should be familiar with an example of the successful use of this technology.
  NOS: Certain potential uses of CRISPR raise ethical issues that must be addressed before implementation. Students should understand that scientists across the world are subject to different regulatory systems. For this reason, there is an international effort to harmonize regulation of the application of genome editing technologies such as CRISPR.
  

• D1.3.10

  Hypotheses to account for conserved or highly conserved sequences in genes

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  Conserved sequences are identical or similar across a species or a group of species; highly conserved sequences are identical or similar over long periods of evolution. One hypothesis for the mechanism is the functional requirements for the gene products and another hypothesis is slower rates of mutation.