12-4 Mutations

12-4 Mutations

• Changes in the genetic material• Kinds of mutation– Gene mutation

• Changes in a single gene

– Chromosomal mutation• Changes in whole chromosome

Gene mutation

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

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

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

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

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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

Example of Genetic disorder

1) Down syndrome• 47, trisomic 21

Example of Genetic disorder

2) Turner syndrome• 45 chromosome, xo

Example of Genetic disorder

3) Klinefelter syndrome– 47, XXY

Example of Genetic disorder

4) Jacob syndrome– 47, XYY

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Examples of polyploidy

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)