Gene mutation Flashcards
What is a mutation?
Any change to the quantity or the base sequence of the DNA.
What is a gene mutation?
Any change to one or more nucleotide bases or change in the sequence of the bases in DNA.
What is base substitution?
Type of gene mutation which a nucleotide in a DNA molecule is replaced by another nucleotide that has a different base.
E.g. GTC, cytosine is replaced by guanine, so it becomes GTG which codes for another amino acid then it would replace the original amino acid.
What harm could base substitution cause?
The polypeptide which it produces will have a different amino acid within and it will depend on the role which the original amino acid. e.g. if it’s responsible for forming bonds in the tertiary structure then the replacement might cause a different bond to be formed.
The protein might be in different shape and not be able to function properly.
What effect of base substitution would cause if the new triplet of bases codes for the same amino acid?
Due to the degenerate nature of the genetic code, if the triplet of bases codes for the same amino acid, there’ll be no change in the polypeptide produced and so the mutation will have no effect.
What is a deletion of bases?
A gene mutation by deletion is when a nucleotide is lost from the normal DNA sequence.
What changes can base deletion cause?
Usually, the amino acid sequence of the polypeptide would be completely different so it might not function properly because the sequence of bases in the DNA is read in units of 3 bases. So one deleted nucleotide causes all triplets in a sequence to shift to the left by one base so it will all be read differently.
What is chromosome mutation?
The change in the structure or number of whole chromosomes.
What are the 2 forms of which chromosome mutation would occur as?
1) Changes in whole sets of chromosomes - Occur when organisms have 3 or more sets of chromosomes rather than 2. The condition is called polyploidy and occurs mostly in plants.
2) Changes in the number of individual chromosomes - When individual homologous pairs of chromosomes fail to separate during meiosis - non-disjunction and usually results in a gamete having either one more or one fewer chromosome. This results in the offspring to have one more or one fewer chromosome than normal e.g. Down’s syndrome where individual has an additional chromosome 21.
What does mutagenic agents do?
Mutagenic agents can increase the rate of gene mutation.
What is a silent mutation?
Occurs when substitution of a base still code for the same amino acid so nothing changes.
What is a nonsense mutation?
A nonsense mutation occurs when substitution of a base occurs leading to a premature ‘stop codon’ being coded for. So this will cause a premature end to the synthesis of a polypeptide. A successful synthesis of the final protein is unlikely so not be able to function properly.
What is a mis-sense mutation?
Occurs when a change in base leads to a different amino acid being coded for.
