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TOPIC 6: MUTATION - Coggle Diagram

- - - - MUTATION THAT ARE SUDDEN AND OCCURS NATURALLY AT A VERY LOW RATE
    - - MUTATION THAT OCCURS DUE TO INTERACTION OF DNA WITH MUTAGENS
  - - - UV RAYS, GAMMA RAYS, X-RAYS
    - - COLCHICINE, ETHIDIUM BROMIDE, MUSTARD GAS
- - - - Two or more pairs of nucleotides are inverted in a nucleotide sequence of a gene.
        
        Effect may not be as severe as frameshift
        mutation (minor phenotype abnormality)
        
        Normal code: AGA - GTC - TTC
        ser - glu - lys
        
        Base inversion: AGA - TGC - TTC
        ser - thr - lys
    - - One or more pairs of nucleotide are removed or deleted from a DNA nucleotide sequence of a gene.
    - - ONE OR MORE PAIRS OF NUCLEOTIDE ARE REPLACED WITH ANOTHER PAIRS OF NUCLEOTIDES IN A SEQEUNCE OF A GENE
        
        THE GENE WILL BE TRANSCRIBED INTO A DIFFERENT mRNA
        
        THE ALTERED mRNA WILL BE TRANSLATED INTO A DIFFERENT POLYPEPTIDE (WITH DIFFERENT AMINO ACID SEQUENCE)
        
        A BASE SUBSTITUTION CHANGES ORIGINAL CODON TO STOP CODON (UAG, UAA, UGA) SHOWS NONSENSE MUTATION
        
        A BASE SUBSTITUTION CHANGES ORIGINAL CODON TO ANOTHER CODON WHICH CODES FOR DIFFERENT AMINO ACID SHOWS MISSENSE MUTATION
        
        A BASE SUBSTITUTION CHANGES ORIGINAL CODON TO ANOTHER CODON WHICH STILL CODES FOR THE SAME AMINO ACID SHOWS SILENT MUTATION
        
        DESCRIBE THE CONSEQUENCES OF BASE SUBSTITUTION (SICKLE CELL ANAEMIA)
        
        mRNA HAS GUG INSTEAD OF GAG
        
        GLUTAMIC ACID (Glu) IS REPLACED WITH VALINE (Val)
        
        ON DNA, T IN CODON CTC IS REPLACED WITH A
        
        EFFECT
        
        Hemoglobin become abnormal (Hb-S), stiff & distorted
        
        Erythrocyte becomes sickle-shaped
        
        The erythrocytes clump together to clog the capillaries and less O2
        is transported
        
        Patient suffers from anaemia: pale, easily tired
        ~ Hb-S stiff & tend to accumulate in small capillaries
    - - One or more nucleotides are inserted into a DNA
        nucleotide sequence of a gene.
        
        The effect of base insertion and base deletion.
        
        The insertion or deletion of one pair of nucleotide (in a gene of DNA) has altered the reading frame of the codons on the mRNA (during translation)
        
        From the point of mutation, the altered codons will be
        translated into different sequence of amino acids
        
        Non-functional protein produced / different protein produced
        
        This mutation is called FRAMESHIFT MUTATION.
- - - - Deletion
        
        The lost of one segment containing one or more genes
        
        E.g.: Cri-du-chat syndrome
        
        Is a genetic, chromosomal disease that resulted from the deletion of
        variable sizes in the short arm of chromosome 5.
        
        The phenotype: ranging from a distinctive cat-like cry to additional
        growth, facial, and mental abnormalities.
      - Inversion
        
        A region of a chromosome breaks off and rotates
        through 180° before rejoining the chromosome
      - Translocation
        
        Involves a region of a chromosome breaking off and rejoining either the other end of the same chromosome or another non-homologous chromosome.
      - Duplication
        
        A region of a chromosome becomes
        duplicated, an additional set of genes exists
    - - Changes that involve either individual chromosome number or set of chromosome number (all genome)
      - May result in abnormalities
      - Error occurs during meiosis
        
        Chromosomes fail to segregate properly
        during meiosis
        
        Due to non-disjunction during meiosis I or
        meiosis II
      - NON-DISJUNCTION
        
        Homologous chromosomes / sister chromatids fail to segregate properly & move to the same pole of the cell
        
        Occurs during anaphase I or anaphase II in meiosis
        
        Produce abnormal gamate (n+1) and (n-1)
      - Types
        
        Aneuploidy
        
        Condition where the diploid cell (2n) gains or losses one or more chromosomes
        
        Involves non-disjunction on a specific individual chromosome only
        
        Caused by abnormalities in the autosome number OR sex
        chromosome number
        
        Can occur in male (during spermatogenesis) or female (during
        oogenesis)
        
        MONOSOMY
        
        One chromosome is missing from a diploid cell / organism / chromosome set
        
        Occurs when abnormal gamete (n-1) fertilises with normal
        gamete (n)
        
        Produces abnormal zygote (2n – 1)
        
        E.g: no. of chromosomes in human = 46 – 1 = 45
        
        TRISOMY
        
        One chromosome is gained / added for a diploid cell / organism
        / chromosome set
        
        Occurs when abnormal gamete (n+1) fertilizes with normal
        gamete (n)
        
        Produces abnormal zygote (2n + 1)
        
        E.g: no. of chromosomes in human = 46 + 1= 47
        
        Down syndrome (Trisomy 21)
        
        Non-disjunction of chromosome 21 during meiosis I or
        II (spermatogenesis or oogenesis)
        
        Produce abnormal gamete that has 1 additional
        chromosome 21 (24 chromosomes)
        
        When the abnormal gamete (n+1=24) fertilizes with a
        normal gamete (n=23)
        
        Abnormal zygote with 3 chromosomes 21 (2n+1=47) /
        Down Syndrome ( Trisomy 21) individual will be produced.
        
        Phenotype
        
        Characteristic facial features
        
        Short stature (about 4 feet tall)
        
        Large, protruding tongue with furrowing
        
        Correctable heart defects
        
        Developmental delays
        
        Euploidy / Polyploidy
        
        Changes of the chromosome number which involved the whole
        chromosome set
        
        Occurred when a set of chromosome did not separate
        during gametogenesis
        
        Common in plants than in animals
        
        AUTOPOLYPLOIDY
        
        Increase in number of chromosomes within the same species
        
        The chromosomes set are homologous with the parent cell
        
        Can be induced using colchicines (inhibit spindle fiber formation)
        
        Examples in plants : strawberries (octoploid, 8n), potato (tetraploid, 4n) & bananas (triploid, 3n)
        
        ALLOPOLYPLOIDY
        
        Chromosome number in a sterile hybrid becomes doubled and produces fertile hybrids
        
        F1 hybrids produced from different species are usually sterile
        
        Examples of Polyploidy Crops
        
        Triploid crops: banana, apple, ginger, watermelon, citrus.
        
        Tetraploid crops: potato, wheat, maize, cotton, tobacco.
        
        Hexaploid crops: chrysanthemum, bread wheat, oat .
        
        Octoploid crops: strawberry, dahlia, sugar cane.