Higher Biology - Unit 1.6

​Unit 1.6

Mutations​

​Mutations

• During cell division occurs the process of DNA replication which is very carefully controlled to preserve the encoded genetic information

​

• However, when a change in the genome occurs (which they sometimes do) ​it is known as a mutation

​Mutations can have 2 results...

​No protein is expressed

​An altered protein is expressed

​Or

​Gene/Chromosome

​There are 2 different types of mutations which can occur...

​Single Gene

Mutations which effect a few bases​

​Chromosome Structure

Mutations which effect the structure of one or more chromosomes​

Multiple Choice

Mutations can occur during...

• DNA replication

• Respiration

Multiple Choice

After a mutation...

• No protein is expressed

• An altered protein is expressed

• Both will happen

• Both are possible

​Single gene mutations

​They involve the alteration of a nucleotide

​This can happen as a result of one of the following:

​1 - The substitution of one nucleotide with another

​

​2 - The insertion of one or more nucleotides into a DNA sequence

​3 - The deletion of one or more nucleotides from a sequence

​Substitution Mutations

​Will result in a change which only effects one codon

​This is known as "point mutation" and the resulting mutation can be one of the three types:

​Missense

Changes the codon so that a different amino acid is produced, may result in the shape of the protein changing causing it to become unable to perform it's function, however, some changes in amino acids won't have a significant effect​

​Splice-site

Effects the boundaries between exons and introns, which are splice sites. This mutation can therefore prevent splicing at that particular site which will result in a very different protein being made. Some exons might stay and introns removed​

​Nonsense

​Changes to codon from an amino acid to a stop codon, resulting in a smaller protein being produced. The short protein is generally non-functional or it's function is effected

​

​Insertion and Deletion Mutations

​These are known as "frame-shift mutations"

• Frame mutations are when codons (group of 3 nucleotides) are read at the ribosome, the codon reading frame is shifted by one codon

• Completely different amino acids are coded for after this mutation

• The resulting protein will be significantly altered and usually non-functional

Multiple Choice

Missense

• Changes the codon so that a different amino acid is produced, and changes the shape

• Changes to codon from an amino acid to a stop codon, resulting in a smaller protein being produced

• Effects the boundaries between exons and introns and can prevent splicing

Multiple Choice

Nonsense

• Changes to codon from an amino acid to a stop codon, resulting in a smaller protein being produced

• Changes the codon so that a different amino acid is produced, and changes the shape

• Effects the boundaries between exons and introns and can prevent splicing

Multiple Choice

Splice-site

• Effects the boundaries between exons and introns and can prevent splicing

• Changes to codon from an amino acid to a stop codon, resulting in a smaller protein being produced

• Changes the codon so that a different amino acid is produced, and changes the shape

Multiple Choice

Substitution mutations fall into which category?

• Point mutations

• Frame-shift mutations

Multiple Choice

Deletion and insertion mutations fall into which category?

• Point Mutations

• Frame-shift mutations

Multiple Choice

What happens after a frameshift mutation?

• The same amino acids are coded

• Completely different amino acids are coded

​Chromosome Structure Mutations

• Chromosome structure mutations effect the shape of whole chromosomes and whole new genes as opposed to individual nucleotides

​

• These mutations can result in errors in cell division, causing a section of a chromosome to break off, be duplicated, or ​move to another chromosome

​Chromosome mutations can result in:

​Deletion - Where a section of a chromosome is removed

​

Translocation - Where a section of a chromosome is added to another chromosome that is not its homologous partner

​

Inversion - Where a section of a chromosome is reversed

​

Duplication - Occurs when a section of chromosome is added from its homologous partner

​

Chromosome mutations are often lethal as the chromosome structure is altered​

​

Multiple Choice

Which of the following is referred to as the chromosome mutation in which a chromosome becomes dislocated and attaches itself to a whole other chromosome?

• Tanslocation

• Deletion

• Substitution

• Insertion

Multiple Choice

Which type of chromosome structure mutation is important for evolution?

• Duplication

• Insertion

• Deletion

• Frame-shift

​List of Terms

Deletion - Mutation involving the loss of a sequence of genes in a chromosome or the loss of a nucleotide from a sequence

Duplication - Chromosome mutation in which a section of chromosomes is added from its homologous partner. Important for evolution

Frame-shift mutation - Single gene mutations which cause all codons and all amino acids after the mutation to be changed

Insertion - Single gene mutation in which an additional nucleotide is placed into a sequence

Inversion - Chromosome mutation in which a set of genes is reversed

Missense - Single gene mutation which results in one amino acid in a protein being changed for another

Non-coding sequence - DNA sequence that does not encode a protein

Nonsense - Single gene mutation which results in a stop codon being produced

Single gene mutations - Mutations which involve in the alteration of a sequence of a DNA nucleotide

Splice-site mutations - Mutations which effect the boundaries between introns and exons, can prevent splicing in effected splice-sites

Substitution - Single gene mutation in which one nucleotide is replaced by another

Translocation - Mutation in which part of a chromosome becomes attached to another whole chromosome​

​

​END OF KEY AREA