mutations

Question 1

Gene mutation

Answer 1

o A change in the sequence of bases of a particular gene

Question 2

Mutation

Answer 2

o plays an important role in evolution  ultimate source of all genetic variation
o important as the first step of evolution because it creates a new DNA sequence for a particular gene, thereby creating a new allele
o harmful BUT are useful in nature and the laboratory as a source of genetic diversity, which makes evolution by natural selection possible
o may result from: errors in DNA replication or recombination OR physical or chemical agents called mutagens

Question 3

Mutagen

Answer 3

o Alters the DNA sequence of the cell

Question 4

types of mutagens

Answer 4

o Chemical mutagens e.g. ethidium bromide and nucleotide analogs
 They work by blocking DNA replication, resulting in a shorter DNA synthesised

o Physical mutagens e.g. high energy radiation such as X-rays and ultraviolet rays
 They damage DNA by breaking it into smaller fragments

o Biological mutagens e.g. Human Papiloma Virus (HPV)
 A virus works by inserting its DNA into the chromosomes/genome of human cells, thereby altering the DNA sequence and disrupting gene functions

Question 5

types of gene mutations

Answer 5

o Nucleotide substitution: the replacement of one nucleotide and its base-pairing partner with another pair
o Nucleotide deletions or insertions: the loss or addition of 1 or more nucleotides

Question 6

result from nucleotide substitution

Answer 6

o Missense mutation
 The new nucleotide alters the codon and hence produces an altered amino acid in the protein

o Nonsense mutation
 The new nucleotide changes a codon that codes for an amino acid to a STOP codon
 Translation of the mRNA will stop prematurely and the protein formed is truncated
 The earlier this occurs in the gene, the more truncated the protein is and the more likely it will be non-functional (misfolding of truncated protein) OR no functional protein is produced (no transcription and/or translation occurred)

o Silent mutation
 They do not cause a change in their resulting polypeptide sequence and proper folding of the protein can still occur
 Most amino acids are encoded by a few different codons (degeneracy of the genetic code)
 For instance, if the third base of valine is changed from the codon GUU to GUC, valine will still be encoded

Question 7

result from nucleus deletions or insertions

Answer 7

o Frameshift mutation
 Alters all subsequent codons (can range from one to thousands) downstream from the mutation site
 Effect can be deleterious, especially when the entire polypeptide sequence is altered
 Effect: change the properties of the protein, particularly its tertiary structure – or to cause no protein to be coded for at all