Mutations Flashcards
What is a gene mutation?
A gene mutation is a change in the DNA base sequence of a chromosome.
When are mutations likely to occur?
Mutations are most likely to occur during DNA replication.
The diagram on the right shows part of a gene that has undergone a series of mutations.
The table below shows some DNA triplets and the amino acids they code for. A substitution mutation has occurred at the nucleotide highlighted in blue.
What effect will this have on the encoded amino acid? Use the table to help you.
ii) Another substitution has occurred in the third nucleotide in the sequence (highlighted in red). What effect would this mutation have on the encoded protein? Explain why.
The substitution will change the encoded amino acid of the triplet from an arginine to a glycine.
ii) The substitution will have no effect on the overall protein because the GCG triplet encodes the same amino acid, alanine, as the GCT triplet. This is an example of the degenerate nature of the genetic code, where some amino acids are coded for by more than one DNA triplet.
A mutation has occured in which the circled nucleotide is deleted. What effect will this have on how the gene is read?
The deletion will cause a shift in the base triplets due to a change in the number of bases present. This will affect how all the subsequent triplets are read after the deletion.
Why are deletion mutations more significant than substitution mutations?
Deletions are more significant than substitutions because deletions always lead to changes in the amino acid sequence whereas substitutions don’t. Deletions also usually result in several amino acids being changed rather than just one.
Two cultures of identical mammalian cells were grown in a laboratory. One culture was exposed to ionising radiation and one culture (the control) was not. All other conditions were kept the same. Analysis showed that the culture that was exposed to the ionising radiation showed significantly more mutations in its DNA than the control culture. Explain why.
There were more DNA base changes in the cells exposed to ionising radiation because ionising radiation is a mutagenic agent. A mutagenic agent increases the rate at which mutations occur.
