Germline Mutation A heritable change in the DNA Occurred in a germ cell and incorporated in every cell of the body. Can be transmitted to the next generation. Germline mutations play a key role in inherited genetic diseases.
Somatic Mutation Alterations in DNA that occur after conception. Occur in any of the cells of the body except germ cell. Can not transmitted to the next generation. These alterations can (but do not always) cause cancer or other diseases.
Mutation Spontaneous/ Induced Affect DNA nucleotide sequence or chromosomal alteration.
Spontaneous Mutation Spontaneous lesions can occur during normal cellular processes, such as; DNA replication (replication error), DNA repair, Chemical alteration of the DNA molecule.
Nucleotide Mismatch can result from: Formation of apurinic or apyrimidinic sites following depurination or depyrimidination reaction. Necleotide conversions involving deamination reactions. Presence of a tautomeric form of an individual nucleotide in replicating DNA.
Deamination Reaction One of the most frequent is the loss of an amino group resulting, for example, in a C being converted to a U.amino group Source:
Induced Mutation Caused by mutagenic agents (Mutagens) Radiation, Chemicals, or Viruses ……
Point Mutation Silent mutation Missense mutation Nonsense mutation
Point Mutation Base substitutions are those mutations in which one base pair is replaced by another. Transition: The replacement of a base by the other base of the same chemical category (purine/ purine; pyrimidine/ pyrimidine). Transversion: The replacement of a base of one chemical category by a base of the other (pyrimidine/ purine; purine/ pyrimidine).
Silent Mutation Single substitution mutation when the change in the DNA base sequence results in a new codon still coding for the same amino acid. Source:
Missense mutation One triplet codon altered, results in one wrong codon and one wrong amino acid. Source:
Missense Mutation Acceptable missense: This occur when single base change results in replacement of one A.A by another with rather same function. Non acceptable missense: This occur when single base change result in the replacement of one amino acid with another with completely different function.
Nonsense Mutation Change a codon that specifies an amino acid into a termination codon lead to shortened protein because translation of the mRNA terminate prematurely. Source:
Sickle Cell Disease It results from a single base change in the gene for B-globin. The altered base cause insertion of the wrong amino acid into one position of B globin protein. These altered protein results in distortion of red blood cells under low oxygen conditions.
Insertion/ Deletion Insertion/deletion can disrupt the grouping of the codons, resulting in a completely different translation. Deletions: Remove information from the gene. A deletion could be as small as a single base or as large as the gene itself. Insertions: Occur when extra DNA is added into an existing gene.
Insertion/ Deletion Multiple of 3 (codon) Deletion or insertion of amino acids in protein. Not multiple of 3
Altered reading frame or fram-shift, altered amino acid sequence, often premature termination of protein through generation of termination codon with loss of function/activity. Source:
Structural Abnormalities Result from: Misrepair of chromosome breaks or Malfunction of the recombination system. Balanced: no net gain or loss of chromosomal material, Example: Translocation, inversion, ring chromosome. UnBalanced: net gain or loss of chromosomal material Example: Loss or duplication of whole chromosome arms or tiny.
Numerical Abnormalities Variations in the chromosome number (heteroploidy) can be mainly of two types: Euploidy Aneuploidy
Variation in Chromosome Number Euploidy: Change in whole chromosome sets. Monoploidy Diploidy Polyploidy Aneuploidy: Changes in part of chromosome sets. An additional or missing chromosome. Hypoploidy: Monosomy, nullisomy Hyperploidy: Trisomy, Tetrasomy
The most common mechanism for aneuploidy is meiotic non-disjunction, the failure of a pair of chromosomes to separate during one of the two meiotic divisions, usually Meiosis I. Polyploidy may occur due to abnormal cell division, either during mitosis, or commonly during metaphase I in meiosis. Triploidy may occur due to dispermy or failure of one of the meiotic divisions. Tetraploidy results mainly from a mitotic error in early cleavage of the zygote.
Effect of Mutation No effect (silent mutation) Beneficial Harmful effect that leads to outright disease or death. Mutation that occur in utero are incompatible with life. Enencephaly.
On rare occasions, a mutation results in a new characteristic which can help the organism survive in unfavorable environmental conditions. The new characteristic will be passed to its offspring who can survive where others may die.
DNA Damage and Mutation
DNA Damage The various forms of spontaneous and induced DNA damage give rise to a different types of molecular mutation: Nucleotide mismatch Large deletion Addition Translocation …
References& Further Reading Bruce Alberts, Alexander Johnson, Julian Lewis, Martin Raff, Keith Roberts, and Peter Walter. Molecular Biology of the cell. ISBN Daniel H. Farkas. DNA Simplified: The Hitchhiker's Guide to DNA. Washington, DC: AACC Press, 1996, ISBN Robert F. Weaver. Molecular Biology. Fourth Edition. McGraw-Hill International Edition. ISBN Robert F. Mueller,Ian D. Young. Emery's Elements of Medical Genetics: ISBN X Griffiths AJF, Gelbart WM, Miller JH, et al. Modern Genetic Analysis. (Internet). New York: W. H. Freeman; rt=objectonlyW. H. Freeman
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