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VICBiologyQuick questions
Unit 4: How does life change and respond to challenges?
Quick questions on Gene and chromosomal mutations (point, frameshift, block, causes and effects): VCE Biology Unit 4
15short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.
What is gene (point) mutations?Show answer
A point mutation changes a single base in the DNA. The three categories are:
What is frameshift mutations?Show answer
A frameshift mutation is an insertion or deletion of a number of bases that is not a multiple of three. The ribosome reads codons in groups of three; adding or removing one or two bases shifts every codon downstream.
What is block (chromosomal) mutations?Show answer
Block mutations affect large segments of a chromosome or whole chromosomes.
What is causes of mutation?Show answer
Errors in DNA replication. DNA polymerase makes about one error per 100,000 bases, then proofreads and corrects most of them. A small number escape repair and become permanent on the next round of replication.
What is consequences for the gene product?Show answer
The effect of a mutation depends on where it occurs and what kind of change it causes:
What is substitution?Show answer
One base replaces another. Substitutions are sub-classified by their effect on the codon and protein:
What is insertion or deletion of one base?Show answer
Adds or removes a single base. This shifts the reading frame and is treated as a frameshift mutation (see below).
What is consequences?Show answer
Every amino acid from the mutation site onward is changed. A premature stop codon usually appears, truncating the protein. The product is almost always non-functional.
What is inversion?Show answer
A segment of chromosome breaks off, flips and rejoins in reverse orientation. Genes within the segment are still present but their order is reversed. May disrupt regulation or split a gene.
What is translocation?Show answer
A segment moves from one chromosome to a non-homologous chromosome. Reciprocal translocations swap segments between two chromosomes. The Philadelphia chromosome (translocation between chromosomes 9 and 22) is associated with chronic myeloid leukaemia.
What is duplication?Show answer
A segment of chromosome is copied so the genes within it appear twice. Duplications are an important source of new genes through evolution, because the extra copy can mutate without losing the original function.
What is deletion?Show answer
A segment of chromosome is lost. Multiple genes are removed. Usually severe (for example, Cri-du-chat syndrome from deletion on chromosome 5).
What is non-disjunction?Show answer
Chromosomes (or chromatids) fail to separate during meiosis. Gametes end up with one chromosome too many or too few. After fertilisation, the zygote is aneuploid.
What is errors in DNA replication?Show answer
DNA polymerase makes about one error per 100,000 bases, then proofreads and corrects most of them. A small number escape repair and become permanent on the next round of replication.
What is spontaneous chemical changes?Show answer
Bases can undergo deamination (cytosine becomes uracil, for instance) or tautomeric shifts that change pairing properties.