Unit 1 Human Cells Higher Human Biology for CfE Miss Aitken Key Area 1.4 – Mutations Unit 1 Human Cells Higher Human Biology for CfE Miss Aitken

Mutations Mutations are random changes to genetic material that result in no protein or an altered protein being synthesised.

Single gene mutations These involve changes to the DNA nucleotide sequence which alters the sequence of bases on the DNA. Three types of single gene mutations exist: Substitution. Insertion. Deletion.

Substitution One nucleotide is removed from a DNA sequence and replaced by another with a different base. e.g Normal ATGTCCATG.....Mutation ATGGCCATG This causes only a change in one amino acid in the protein and is called a missense. However, if it causes the production or loss of a stop codon this has a bigger impact and is called a nonsense.

Insertion An additional nucleotide is added into a DNA sequence. Normal ATGTCCATG.....Mutation ATGTGCCATG This has a major effect on the protein made since all amino acids after the mutation are affected. Result in a frameshift mutation.

Deletion A nucleotide is removed from the DNA sequence. Normal ATGTCCATG.....Mutation ATGCCATG Like insertion mutations, a deletion mutation has a major effect on the protein made since all amino acids after the mutation are affected. Also result in a frameshift mutation.

Splice Site Mutations A mutation at a splice site could result in an intron being left in the mature mRNA and so contributing to protein structure. This would result in a protein that would not function normally.

Examples of Gene Mutation Some well-known inherited genetic disorders include cystic fibrosis, sickle cell anemia, Tay-Sachs disease, phenylketonuria (PKU) and colour-blindness, among many others. All of these disorders are caused by the mutation of a single gene.

Chromosome Mutations Some mutations affect the structure of chromosomes present in our cells. These happen because chromosomes break off and are lost, or join back on in a different way. Chromosome mutations are often lethal. Others give rise to serious health complications.

Types of Chromosome Mutation Deletion - parts of a chromosome are completely missing e.g. Cri du Chat syndrome involves the loss of part of chromosome 5 Duplication – A set of genes on one chromosome becomes attached to another chromosome, leading to repeated genes e.g. many types of inherited cancer Inversion - A section of chromosome becomes reversed Translocation – Detached genes become attached to a different chromosome e.g. some types of lymphoma are caused by a translocation on chromosome 14