Mutations

SQA Higher Biology 2022

❥ Nonsense mutations

❥ Nonsense mutations

________- these substitutions change the codon from an amino acid to a premature stop codon.

Duplication

________ is where a section of a chromosome is added from its homologous partner.

Mutations Mutations

________ are changes in DNA that can result in no protein or an altered protein being synthesised.

❥ deletion

________ is where a section of a chromosome is Chromosome structure mutations can be one of four types: removed.

❥ inversion

________ is where a section of a chromosome is reversed.

Point Mutations Substitutions

________ result in a change that only affect one codon.

Single Gene Mutations Single gene mutations involve the alteration of a DNA nucleotide sequence as a result of

❥ the substitution of one nucleotide with another ❥ the insertion of one or more nucleotides into a DNA sequence ❥ the deletion of one or more nucleotides from a sequence

❥ Nonsense mutations

these substitutions change the codon from an amino acid to a premature stop codon

❥ Splice-site mutations

these substitutions result in some introns being retained and/or some exons not being included in the mature transcript

❥ deletion is where a section of a chromosome is Chromosome structure mutations can be one of four types

removed

What are mutations?

Mutations are changes in DNA that can result in no protein or an altered protein being synthesised.

What do single gene mutations involve? What are they the result of?

Single gene mutations involve the alteration of a DNA nucleotide sequence as a result of substitution, insertion or deletion.

What is a substitution mutation?

The substitution of one nucleotide with another.

What is an insertion mutation?

The insertion of one or more nucleotides into a DNA sequence.

What is a deletion mutation?

The deletion of one or more nucleotides from a

sequence.

What do substitutions result in? What is this known as?

Substitutions result in a change that only affect one codon. This is known as a point mutation.

What are the three types of point mutations?

Missense, nonsense and splice-site mutations.

What is a missense mutation?

These substitutions change the codon so that one amino acid is changed for another. This may result in a non-functional protein or may have little effect on the protein depending on the amino acid that has been changed.

What is a nonsense mutation?

These substitutions change the codon from an amino acid to a premature stop codon. This results in a shorter protein being produced. The shortened protein is generally non-functional or its function is affected.

What are splice-site mutations?

These substitutions result in some introns being retained and/or some exons not being included in the mature transcript.

What is a frame-shift mutation?

The effect of an insertion or deletion of a nucleotide results in frame shift mutations. This means that when the groups of three nucleotides (codons) are read at the ribosome, the codon reading frame is shifted by one codon.

What do frame-shift mutations cause?

Frame shift mutations cause all of the codons and all of the amino acids after the mutation to be changed. This has a major effect on the structure of the protein produced.

What are chromosome structure mutations?

Chromosome structure mutations are alterations that affect whole chromosomes and whole genes rather than just individual nucleotides.

What do chromosome structure mutations result from?

These mutations result from errors in cell division that cause a section of a chromosome to break off, be duplicated or move onto another chromosome.

What are the four types of chromosome structure mutations?

Deletion, translocation, inversion and duplication.

What is a deletion chromosome structure mutation?

Deletion is where a section of a chromosome is removed.

What is a translocation chromosome structure mutation?

Translocation is where a section of a chromosome is added to a chromosome that is not its homologous partner.

What is an inversion chromosome structure mutation?

Inversion is where a section of a chromosome is reversed.

What is a duplication chromosome structure mutation?

Duplication is where a section of a chromosome is added from its homologous partner.

What do the substantial changes in chromosome mutations often make them? Why?

The substantial changes in chromosome mutations often make them lethal as the chromosome structure is altered.

What do chromosomal duplications allow? How does this work?

Duplication allows potential beneficial mutations to occur in duplicated gene whilst the original gene can still be expressed to produce its protein. For example, the chromosome still has the original gene and so produces the correct protein. However, the duplicated mutation may also produce another protein/characteristic that gives the organism a select advantage over others without any negative consequences.