Single gene mutations

Question 1

Single Gene Mutations definition

Answer 1

Alteration of a DNA nucleotide sequence as a result of either substitution, insertion or deletion of nucleotides.
Also referred to as point mutations when a single nucleotide is added, changed or deleted.

Question 2

Single gene mutation: substitution

Answer 2

A nucleotide is swapped for another. A nucleotide is removed from the sequence and replaced by one with a different base.
Do not result in frameshift mutations

Question 3

Single gene mutation: Insertion

Answer 3

One or more nucleotides are “inserted” into a section of DNA. At one additional nucleotide is added to the sequence.
Will result in a frame shift unless a multiple of 3 of nucleotides are added.

Question 4

Single gene mutations: deletion

Answer 4

One or more nucleotides are “deleted” in a section of DNA. At least on nucleotide is removed from the sequence and not replaced by another.
Will result in a frame shift mutation unless a multiple of 3 nucleotides are deleted.

Question 5

Frameshift Mutations

Answer 5

Insertion or deletion of a nucleotide results in frameshift mutations.
All bases downstream are moved from their place, this alters all of the codons from the mutation onwards thus all amino acids are changed.
This has a major effect on the protein produced.
Won’t happen if a multiple of 3 nucleotide are either added or deleted, (cannot be a mixture of the two I.e 2 deleted on inserted)

Question 6

Classification of substitution mutations

Answer 6

Nucleotide substitution can be further classified into missense mutations, nonsense mutations, splice site mutations, silent mutations and neutral mutations.

Question 7

Missense Mutations

Answer 7

Following the substitution, the altered DNA codon codes for an amino acid - the code make sense but not the original sense. A single different amino acid is made.
The effect of this varies - proteins could be non functional or it could have little effect on the protein.

Question 8

Nonsense mutations

Answer 8

Following a substitution, a codon which used to code for an amino acid becomes changed to one which codes for a stop codon. Consequently protein synthesis will be stopped prematurely and a shorter polypeptide will be produced as a result.
This will either form a non functioning protein or a differing one.

Question 9

Silent mutation

Answer 9

A nucleotide has been substituted however then new triplet codes for the same amino acid as such the protein is normal.

Question 10

Neutral mutation

Answer 10

The substituted nucleotide results in a triplet that codes for a different amino acid. However this amino acid is similar to the original. This means the mutated protein functions normally.

Question 11

Splice site mutations

Answer 11

Mutations in the are that marks the start or end of an intron may lead to one or more introns remain in the mature mRNA transcript.
Also some exons may not be included in the mature transcript.
This will lead to the creation of a protein that does not function properly.

Question 12

Evolutionary importance of gene mutation

Answer 12

Mutation is the only source of variation - new alleles of a gene.
On occasion this mutated allele will provide a selective advantageous to the individual - therefore they will be more likely to reproduce and pass on they gene to their offspring via reproduction.
In the end this gene will increase in frequency within the population to the detriment of less desirable alleles - consequently the population evolves.