D1.3 Mutation and gene editing

Question 1

D1.3.1—Gene mutations as structural changes to genes at the molecular level

Answer 1

Distinguish between substitutions, insertions and deletions.

Question 2

D1.3.2—Consequences of base substitutions

Answer 2

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.

Question 3

D1.3.3—Consequences of insertions and deletions

Answer 3

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

Question 4

D1.3.4—Causes of gene mutation

Answer 4

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.

Question 5

D1.3.5—Randomness in mutation

Answer 5

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

Question 6

D1.3.6—Consequences of mutation in germ cells and somatic cells

Answer 6

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

Question 7

D1.3.7—Mutation as a source of genetic variation

Answer 7

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.

Question 8

D1.3.8—Gene knockout as a technique for investigating the function of a gene by changing it to make it
inoperative

Answer 8

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.

Question 9

D1.3.9—Use of the CRISPR sequences and the enzyme Cas9 in gene editing

Answer 9

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

Question 10

D1.3.10—Hypotheses to account for conserved or highly conserved sequences in genes

Answer 10

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.