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Ch . 12 Notes

Ch . 12 Notes. Gene Mutations. A mutation is change in a DNA sequence that is present in < 1% of a population May occur at the DNA or chromosome level A polymorphism is a genetic change that is present in > 1% of a population The effect of mutations vary

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Ch . 12 Notes

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  1. Ch. 12 Notes Gene Mutations

  2. A mutation is change in a DNA sequence that is present in < 1% of a population May occur at the DNA or chromosome level A polymorphism is a genetic change that is present in > 1% of a population The effect of mutations vary “Loss-of-function” mutations – Recessive “Gain-of-function” mutations – Dominant Mutations are important to evolution Our evolutionary relatedness to other species allows us to study many mutations in non-human species The Nature of Mutations

  3. A mutation is a change in a gene's nucleotide base sequence. • Molecular mutations (ch. 12) • substituting one base for another • adding or deleting bases • Chromosomal mutations (ch. 13) • chromosomes exchange parts • genetic material jumps from one chromosome to another

  4. Molecular mutations can occur: • in the part of a gene that encodes a protein • at a site critical to intron removal and exon splicing • in a sequence that controls transcription

  5. Effects of mutations: • completely halt production of protein • lower amount of protein • overproduce it • impair protein function • nothing at all • improve gene function

  6. Effects of Mutations

  7. Key Terms • Mutation refers to genotype (altered DNA) • Mutant refers to an unusual phenotype (unusual trait) • Usually connotes an abnormal or unusual, or even uncommon variant that is nevertheless “normal” • Germline mutation • (only in sex cells-gametes) Hereditary • Originate in meiosis • Affect all cells of an individual • Somatic mutation • Originate in mitosis • Affect only cells that descend from changed cell

  8. Causes of Mutation • Spontaneous Mutation • not caused by a known exposure to a mutagen (chemicals that induce mutations) • usually originates as an error in DNA replication • the rate varies from gene to gene (1 in 100,000 bases overall) • bacteria and viruses have higher spontaneous mutation rate

  9. Mutation Hot Spots - mutations are more likely to occur when: • - DNA sequence is repetitive • AAAAAAA • CGCGCGCG • TACTACTAC

  10. Inverted repeat- causes complemantarypairing within a strand

  11. Palindrome (read the same in opposite directions on comp. strands) • GAATTC • CTTAAG

  12. 12.3: Types of Mutations • Point Mutation - change in a single DNA base • Transition- purine replaces purine (A <->G or C<->T) • Transversion- purine replaces a pyrimidine or vice versa (A or G to T or C)

  13. Missense - point mutation that changes a codon for a particular amino acid to a codon for a different amino acid

  14. Nonsense - A point mutation that changes a codon for a particular amino acid into a "stop' codon (UAA, UAG, UGA in mRNA)

  15. Frameshift - disruption in gene's reading frame • deletion- removal base(s) • insertion- addition base(s) • tandem duplication insertion of a large section of a gene (Ex: 1.5 million base pairs)

  16. Deletion of single nucleotide causes a frameshift. Faulty protein makes people extremely susceptible to HPV (warts)

  17. Types of Mutations

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