Mutations SBI 4 U November 23 rd 2012
Mutations SBI 4 U November 23 rd, 2012
What are Genetic Mutations? �Changes in the DNA sequence caused by various mechanisms �Mechanisms of change: synthetic chemicals, radiation, incorrect replication, and random mutations �Beneficial vs. harmful
Genetic Mutations �Small Scale �Large Scale
Small Scale Mutations �Small-scale mutations: mutations of an individual base pair (point mutations) or of small groups of base pairs � 3 types: -substitution -insertion/deletion -inversion
Point Mutations of an individual base pair 3 Types: �Substitution of one base for another �Insertion or deletion of a single base pair �Inversion of two adjoining base pairs Effects of small-scale mutations can range from being positive to none to severe!
Small-Scale Mutations Can be functionally divided into 4 categories: �Missense mutations �Nonsense mutations �Silent mutations �Frameshift mutations
Missense Mutation �Missense mutation: when a change of a single base pair or group of base pairs results in the code for a difference amino acid �May be non-functional or functional (differently)
Missense Mutation �Ex: sickle cell disease �Hemoglobin molecule altered – sickle shape of RBCs �Replacement of A by T – makes valine instead of glutamic acid
Nonsense Mutation �Nonsense Mutation: occurs when the change of a single base pair or group of base pairs results in a premature stop code in the gene �Unable to function
Nonsense Mutation �Ex: Cystic fibrosis �Only 493 amino acids produced instead of 1480 (in some cases)
Silent Mutation �Silent mutation: occurs when the change in one or more base pairs does not affect the functioning of the gene. �Resulting protein not altered!
Frameshift Mutation �Frameshift mutation: occurs when one or more nucleotides are inserted into or deleted from a DNA sequence, causing the reading frame of codons to shift in one direction or the other �Multiple missense and nonsense mutations �Ex: Tay Sachs disease
Large-Scale Mutations �Large-scale mutations involve multiple nucleotides, entire genes, or whole regions of chromosomes �Entire coding regions of DNA may be removed – ex: Dystrophin and Duchenne muscular dystrophy
Large-Scale Mutations �Chromosomal translocation: entire genes or groups are moved from one chromosome to another �Inversion: reversal of direction in the genome �Trinucleotide repeats triplet of nucleotides repeat uncontrollably - - CAG CAG CAG Ex: Huntington’s disease
Causes of Mutations �Spontaneous: arise from inaccurate DNA replication �Induced: environmentally caused
Induced Mutations �Caused by a mutagen, that directly alters the DNA within a cell � 2 types of mutagens: chemicals and radiation
Chemical Mutagens �Any chemical agent that can enter cell nucleus and chemically alter the structure of the DNA �Ex: tobacco smoke and exhaust fumes
Chemical Mutagens �How do they cause mutations? Some mimic a DNA nucleotide. Ex: ethidium bromide inserts itself between the strands of the double helix and alters structure of DNA
Radiation �Lower energy radiation such as ultraviolet B can cause bonds to form between adjacent nucleotides – making a kink - - ex: skin cancer �Higher energy radiation – breaks bonds within the DNA molecule re-arrangement or deletion of large portions of chromosomes. Ex: x-rays can lead to tumours
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