Mutations (Ch 13.3)

Types of Mutations Mutation: heritable changes in genetic information Remember there is a checking system to stop mutations, but not all errors can be caught Two Categories of Mutations Gene mutations: produce changes in a single gene (plant height) Chromosomal mutations: produce changes in whole chromosomes (multiple genes)

Gene Mutations Point Mutations: gene mutations that involve changes in one or a few nucleotides because they occur at a single point in the DNA sequence These mutations occur during replication One cell is altered = all cells replicated from that cell is altered Three types: Substitutions Insertions Deletions

Gene Mutations Substitutions One base is changed to a different base (substituted) It only changes one amino acid normally Sometimes it will change the amino acid and sometimes it will not (remember many different codons can code for a single amino acid) Example: CCC → CCA = proline to proline CCC → ACC = proline to threonine

Gene Mutations Insertions / Deletions One base is inserted or deleted from the DNA sequence If a base is added or deleted it shifts the codon triplets and drastically affects the amino acids Frameshift mutations: they shift the reading frame of the genetic message They can alter the protein so much that it will not be able to perform its function Insertion

Chromosomal Mutations Chromosomal mutations: involve changes in the number or structure of chromosomes Changes location of genes on chromosomes or the copies of some genes Four Types: Deletion: the loss of a chromosome Duplication: an extra copy of part or all of the chromosome Inversion: reverses the direction of parts of a chromosome Translocation: part of one chromosome breaks off and attaches to another chromosome

Effects of Mutations Mutations may or may not affect the organism depending on the type of mutation Most mutations occur in DNA replication Stressful environmental conditions could influence mutation rates (50% genes + 50% environment) Mutagens: chemical or physical agents in the environment Cells can sometimes repair the damages, but sometimes they remain permanent Examples: chemical = tobacco smoke / physical = X-rays

Beneficial Effects of Mutations Mutations often produce proteins with new or altered functions that can be useful to organisms in a changing environment Examples: Insects resisting pesticides Humans resist HIV Humans increase bone strength Plants chromosomes fail to separate during meiosis → triploid (3N) or tetraploid (4N) organisms (polyploidy) = larger and stronger

Harmful Effects of Mutations Sickle Cell Disease defective allele in hemoglobin the oxygen carrying protein in red blood cells makes hemoglobin stick together when the oxygen levels decrease Sickle cell shape gets stuck in the capillaries and damages cells, tissues, and organs Cystic Fibrosis (CF) Deletion of the amino acid phenylalanine Need two copies of CF allele to affect the person (recessive) CF causes digestive problems and produces thick mucus that clogs their breathing passageways

Harmful Effects of Mutations Huntington’s Disease Caused by a dominant allele for protein found in brain cells CAG = glutamine = repeated over and over again Effects Mental deterioration Uncontrollable movement Greater the number of codons the earlier the disease appears and the more severe the symptoms