# Genetic Mutations The two basic categories of DNA mutations are: 1. Single Nucleotide Substitution 2. Frame Shift (changes the frame set by the start codon for [[Translation|translation]]) - Silent Mutation: - Missense Mutation - Nonsense Mutation ## Types of Mutations ### Single Nucleotide Mutations Point Mutations **Transition vs Transversion** - transversion: pyramidine to purine - transition: purine to purine **Nonsense:** Changes the DNA sequence to a stop codon to generate a shorter polypeptide **Missense:** Changes the DNA sequence to a codon that specifies a different amino acid from wild time **Silent:** Changes the DNA sequence to a codon that specifies the same amino acid as wild type ### Frame Shift Mutations Changes the DNA sequence by inserting or deleting a few bases to generate a polypeptide from the wrong reading frame Deletion Insertion “In-Del” > If exactly three nucleotides are inserted/deleted then only a single amino acid will be inserted/deleted rather than the entire frame of the translation process being changed ### DNA Slippage ![[Pasted image 20240329003044.png|500]] ## Causes of Mutations A **mutagen** is any agent that damages DNA, alters its chemistry, or in some way interferes with its functioning and increases the likelyhood of mutations occuring Possible causes of spontaneous mutations include: - errors in DNA replication - mobile genetic elements - spontaneous lesions in DNA Chemical Mutagens: Any agent that damages DNA, alters its chemistry - Base analogues - DNA-modifying agents - Intercalating agents ## Impacts of Mutations **Somatic mutations** that occur within body cells will not be transferred onto offspring. - The impact of the mutation on the organism depends on when it had occurred during their lifespan (with mutations during early development being the most impactful) **Germ-line mutations** that occur within the reproductive cells (sperm or eggs) will be passed onto their offspring --- ## Genomic Variations Inside an Organism - **Mosaicism:** Occurs when a person has two or more genetically different sets of cells in his or her body - **Microchimerism:** The existence of a low-level allogeneic cell population within a host. - spontaneously (dizygotic twins) - iatrogenically (after [[Transplants & Transfusions|tranfusion/transplantation]]) - **Chimerism:** aaa - Ex: fraternal twins fusing to develop into one person