CHAPTER 7: MUTATION
Explain mutation
• A mutation is a change in the amount, arrangement or structure of the DNA of an organism.
• Mutations produce sudden and distinct differences between individuals cause alternation of
chromosome.
• Alteration of chromosome number or structure cause some genetic disorders such as Sickle Cell
Anemia and Down Syndrome
• Mutation can occurring in gamete cells or somatic cells.
i) gamete cells
are inherited, It passed to subsequent generations as part of the hereditary endowment of the
games derived from that cell.
ii) somatic cells
can only be inherited by daughter cells produced by mitosis.
• A mutant is an individual or new genetic character arising or resulting from an instance of mutation the
blue lobster is an example of a mutant.
• Type of mutation
i) spontaneous mutation
- Mistakes happen spontaneously during DNA replication, repair and recombination
- eg. nondisjunction
ii) induced mutation
- Organism exposed to mutagen
What is mutagen ?
• a mutagen is a physical or chemical agent that changes the genetic material
• Operate either by causing changes in the DNA of the genes or by causing chromosome damage
• type of mutagen
i) Physical agent
Ultraviolet ray
Ionizing radiation (X-ray, gamma ray, alpha particles, neutron and electron)
ii) Chemical agent
eg. Colchicine (usually to treat rheumatic complaints, especially gout)
Ethidium bromide
CLASSIFICATION OF MUTATION:
GENE MUTATION (POINT MUTATION)
• Producing alterations in the sequence of DNA nucleotide.
• involve only one or a few base pair in the coding sequence.
• Arise due to spontaneous pairing errors that occur during DNA replication,
• Arise due to mutagens like radiation or chemicals cause damage to the DNA.
• As a result :
- Change the amino acid sequence and thus, changes the protein
- Different protein produced as the effect of mutation may not function as normal
• Classify gene mutation
i) Base substitution
ii) Base insertion
iii) Base deletion
iv) Base inversion
• mutation of base deletion and insertion make cause frame shift mutation
• Alteration of gene mutation cause some genetic disorders such as Sickle Cell Anemia
Classification of Gene mutation:
Base substitution :
• One or a few base pairs in the nucleotide sequences in genes is substitute
• Changes in base sequence – results in changes of codon (UAU/UGU)
• 3 base/ nucleic acid = 1 codon (coding for 1 amino acid)
• Changes in codon:-
a) amino acid changes (missense mutation)
b) changes a codon to stop codon (nonsense mutation)
• Missense mutations are those that still code for an amino acid but change the indicated amino acid eg.
Sickle Cell Anemia.
• Nonsense mutations change an amino acid codon into a stop codon, nearly always leading to a
nonfunctional protein.
Sickle cell Anemia
• mutant Hbs cause defective red blood cell. The cells are shaped like a crescent or sickle
• occurs more commonly in people regions where malaria is or was common. there is a survival value in
carrying only a single sickle-cell gene Those with only one of the two alleles of the sickle-cell disease are
more resistant to malaria, since the infestation of the malaria plasmodium is halted by the sickling of the
cells which it infests.
• sickle shape body produces abnormally shaped red blood cells.
• Hbs stiff & tend to accumulate in small capillary, Hb is not efficient of transporting oxygen
Base deletions
• Loss of 1 or a few base pairs in the nucleotide sequences in genes
• mutation of base deletion make cause frame shift mutation
Normal Mutant
lost of T base during replication of DNA
DNA chain AGA GTC TTC AGA GCT TCG
transcript
mRNA UCU CAG AAG UCU CGA AGC
translation
code of amino acid Ser Gln Lys Ser Arg Ser
frame-shift happen
Base inversion
• 2 base pairs or more are inverted in nucleotide sequence
Normal Mutant
inverted in nucleotide sequence
DNA chain AGA GTC TTC AGA TGC TTC
transcript
mRNA UCU CAG AAG UCU ACG AAG
translation
code of amino acid Ser Gln Lys Ser Thr Lys
Frame-shift Mutations
• Involve insertion/deletion of a base pair or more into the nucleotides sequence of DNA
• Many of these deletions/insertion start in the middle of a codon
• Shifting the reading frame by one or two bases
• Frame shift mutations cause the gene to be read in the wrong three base groups (codon)
• From the mutation point,
• It abrupt the coding sequence of amino acid.
• Changes in codons results in changes in amino acids
• Different polypeptide is produced
• Effect ~ usually harmful to human
• E.g.: Major Thalasemia (mutant homozygote alleles)
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