12-4
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12-4 Mutations
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12-4 Mutations
• Changes in the genetic material• Kinds of mutation– Gene mutation
• Changes in a single gene
– Chromosomal mutation• Changes in whole chromosome
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Gene mutation
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Gene mutation
• Types– Point mutation: changes in one nucleotide
• Single base substitution• Single base insertion• Single base deletion
– Frame shift mutation: changes in nucleotides leads to the shift of reading frame (grouping of the codons) • Insertion• Deletion
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Substitution GGTCACCTCACGCCA ↓
CCAGUGGAGUGCGGUmRNA codons
↓Pro-Arg-Glu-Cys-Gly
Amino acids
Insertion GGTGCTCCTCACGCCA↓
CCACGAGGAGUGCGGU ↓
Pro-Arg-Gly-Val-Arg
DeletionGGTCCCTCACGCCA
↓CCAGGGAGUGCGGU
↓Pro-Gly-Ser-Ala-Val
Normal geneGGTCTCCTCACGCCA
↓CCAGAGGAGUGCGGU
mRNA codons ↓
Pro-Glu-Glu-Cys-GlyAmino acids
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Chromosomal mutation
Structure change
Number change
aneuploidy
polyploidy
Changes in chromosomes
1.duplication 2.inversion3.translocation4.deletion
Have one extra or one less chromosome (2n+1,2n-1)
Have three or more sets of each type of chromosome (3n, 4n)
Caused by nondisjunction
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Non-disjunction
• Fails to separate chromosomes in meiosis 1 or 2• Gametes become n-1 or n+1
XX
X
X
XX
l l
ll
ll ll
Normal
meiosis 1
Non-disjunction
in meiosis 1
Normal meiosis 2
Normal meiosis 2
Non-disjunction in meiosis 2
back
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Significance of mutation
• Most are neutral• Some are harmful– Cause human genetic disorders– Cause some types of cancers
• Some are beneficial– Polyploidy plants are larger and stronger – Mutations lead to evolution in living organisms
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Example of Genetic disorder
1) Down syndrome• 47, trisomic 21
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Example of Genetic disorder
2) Turner syndrome• 45 chromosome, xo
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Example of Genetic disorder
3) Klinefelter syndrome– 47, XXY
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Example of Genetic disorder
4) Jacob syndrome– 47, XYY
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Examples of polyploidy
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Examples of polyploid crops• Triploid crops(3n): apple, banana, citrus, ginger, watermelon• Tetraploid(4n) crops: apple, durum or macaroni wheat, cotton, potato, cabbage, leek, tobacco, peanut, kinnow, Pelargonium • Hexaploid crops(6n): chrysanthemum, bread wheat, triticale, oat, kiwifruit • Octaploid crops(8n): strawberry, dahlia, pansies, sugar cane, oca (Oxalis tuberosa)