Higher Biology Chapter 16 Gene Mutations

This type of mutation involves a change in one or more of the nucleotides in a strand of DNA. There are four types of gene mutation: 1.Substitution of a nucleotide. 2.Inversion of two or more nucleotides. 3.Deletion of a nucleotide. 4.Insertion of a nucleotide.

In all of these cases one or more codons for one or more particular amino acids have become altered. This in turn leads to a change in the protein which is synthesised. For a protein to work properly it must have the correct sequence of amino acids.

Gene Mutations This type of mutation involves a change in one or more of the nucleotides in a strand of DNA. There are four types of gene mutation: 1.Substitution of a nucleotide. 2.Inversion of two or more nucleotides. 3.Deletion of a nucleotide. 4.Insertion of a nucleotide.

Substitution

Gene Mutations This type of mutation involves a change in one or more of the nucleotides in a strand of DNA. There are four types of gene mutation: 1.Substitution of a nucleotide. 2.Inversion of two or more nucleotides. 3.Deletion of a nucleotide. 4.Insertion of a nucleotide.

Inversion of Two or More Nucleotides

“Point” Mutations Substitution and inversion are known as “point” mutations. These bring about minor changes as only one amino acid is affected. Sometimes the organism is affected slightly or not at all. However when the substituted amino acid occurs at a critical position in the protein then a major defect may arise. (Sickle cell anaemia)

Gene Mutations This type of mutation involves a change in one or more of the nucleotides in a strand of DNA. There are four types of gene mutation: 1.Substitution of a nucleotide. 2.Inversion of two or more nucleotides. 3.Deletion of a nucleotide. 4.Insertion of a nucleotide.

Deletion of a Nucleotide

Gene Mutations This type of mutation involves a change in one or more of the nucleotides in a strand of DNA. There are four types of gene mutation: 1.Substitution of a nucleotide. 2.Inversion of two or more nucleotides. 3.Deletion of a nucleotide. 4.Insertion of a nucleotide.

Insertion of a Nucleotide

‘Frameshift’ Mutations Insertion and deletion gene mutations are known as ‘frameshift’ mutations. These mutations lead to major changes as they cause a large portion of the gene’s DNA to be misread. The proteins produced differ from the normal proteins by many amino acids and tend to be non- functional. If these proteins are enzymes which catalyse essential steps in the metabolic pathway, the pathway will become disrupted. (PKU)

Gene Mutations Since most proteins are indispensible to the organism, most gene mutations produce an inferior version of the phenotype. If these changes result in death (eg. albino plants) then the altered gene is said to be lethal.