mutation: an overview salwa hassan teama. m.r.c. ain shams university/ cairo/ egypt

Mutation: An OverviewSalwa Hassan Teama .

M.R.C. Ain Shams University/ Cairo/ Egypt

Mutation

A mutation is a change n genetic material.

A mutation is a change in the DNA sequence or arrangement of DNA.

Mutation

Hereditary mutation (Germline mutations) Acquired (somatic Mutations)

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.

Source: bsw3.naist.jp

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.

Source: http://www.atdbio.com/content/56/Epigenetics:

Induced Mutation

Caused by mutagenic agents (Mutagens) Radiation, Chemicals, or Viruses……

Source: http://www.sciencedirect.com/science/article/pii/S1044579X04000537

Source: http://scienceofacne.com/how-do-bacteria-become-resistant-to-antibiotics/dna-damage-and-mutations-from-uv-exposure-friedberg

Mutation

Gene Mutation

Point Mutation

Insertion/

Deletion

Chromosomal

Alteration

Structural Numerical

Gene Mutation

Point MutationDeletion/Insertion

n

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: http://www.ebi.ac.uk/2can/disease/genes5.html

Missense mutation

One triplet codon altered, results in one wrong codon and one wrong amino acid.

Source: http://www.ebi.ac.uk/2can/disease/genes5.html

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: http://www.ebi.ac.uk/2can/disease/genes5.html

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

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: http://www.ebi.ac.uk/2can/disease/genes5.html

Source: http://homepage.usask.ca/~vim458/advirol/SPCV/evolution/evolution.html

Chromosomal Mutation

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 materialExample: Loss or duplication of whole chromosome arms or tiny.

Source: http://www.ceessentials.net/article3.html

Source: http://www.goldiesroom.org/Note%20Packets/19%20Applied%20Genetics/00%20Applied%20Genetics--WHOLE.htm

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, nullisomyHyperploidy: 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.

Source: http://superphotoscannerwallpaper.blogspot.com/2012/10/chromosomal-disorders.html

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

Source: http://www.sciencedirect.com/science/article/pii/S1934590910007071

DNA Damage

The various forms of spontaneous and induced DNA damage give rise to a different types of molecular mutation:

Nucleotide mismatchLarge deletionAddition Translocation…

Source: http://mulicia.pixnet.net/blog/post/24418728-sources-and-consequences-of-dna-damage

References& Further Reading

Bruce Alberts, Alexander Johnson, Julian Lewis, Martin Raff, Keith Roberts, and Peter Walter. Molecular Biology of the cell. ISBN. 9780815341055

Daniel H. Farkas. DNA Simplified: The Hitchhiker's Guide to DNA. Washington, DC: AACC Press, 1996, ISBN 0-915274-84-1.

Robert F. Weaver. Molecular Biology. Fourth Edition. McGraw-Hill International Edition. ISBN 978-0-07-110216-2

Robert F. Mueller,Ian D. Young. Emery's Elements of Medical Genetics: ISBN. 044307125X

Griffiths AJF, Gelbart WM, Miller JH, et al. Modern Genetic Analysis. (Internet). New York: W. H. Freeman; 1999. http://www.ncbi.nlm.nih.gov/books/NBK21322/table/A998/?report=objectonly

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