Genetic Mutations

1. Genetic Mutations Unit 4 – Lecture 4

2. Mutations • Genetic Mutation – a change in the amount or structure of genetic material of an organism • Mutations can be in DNA or can be chromosomal • Mutations can happen more than once in a sequence [and typically do] • Causes: • mutagens – radiation or chemical substances that increase the rate of mutations

3. Mutations • [Causes:] • problem during interphase when DNA is being replicated • problems are typically noticed and repaired by enzymes during growth • typically mismatch in base pairing • problem in DNA  problem in mRNA  problem in protein synthesis

4. Effects of Mutations • ALL known mutations are harmful overall • some are beneficial under certain circumstances • antibiotic resistance: • immunity to antibiotics • often slow reproduction • often poor acquisition of resources

5. Effects of Mutations • ALL known mutations are harmful overall • some are beneficial under certain circumstances • sickle-cell anemia: • less likely to get malaria • obstruction of blood vessels • organ damage • life span 42-48yrs old

6. Effects of Mutations • Small changes: • may cause no change in the a.as formed • may cause a change in the a.as formed • may cause MASSIVE change in the a.asformed • Large changes…are of course, typically worse than small changes

7. Effects of Mutations • Can cause cancers, genetic disorders • Mutations in cells: • in gametes – passed to the next generation • in somatic cells – not passed on to next generation

8. Discuss • What are substances that cause mutations called? • A mutation in a _____ cell will be passed on to offspring, but a mutation in a _____ cell will NOT be passed on to offspring.

9. DNA Mutations • 3 types (1) – BY CAUSE • substitution – change of a single base from one kind to another [aka point mutation] • ex: THE DOG RAN OUT  THE FOG RAN OUT • may or may not alter the amino acid formed: • CAU & CAC both code for Histidine • CAA & CAG both code for Glutamine • UUU = phenylalanineUUA = leucine

10. DNA Mutations • 3 types (2) – BY CAUSE • deletion – a single base is deleted from the sequence • THE DOG RAN OUT  THE OGR ANO UT • changes the sequence of codons – usually quite a bit; but may not change sequence if next letters code for same thing [like near end] • TAC – UUA – UAA  TAC – UUU – AA • Met – Leu – [stop]  Met – Phe –

11. DNA Mutations • 3 types (3) – BY CAUSE • insertion – a single base is added to the sequence • THE DOG RAN OUT  THE DOG RAF NOU T • changes the sequence of codons – usually quite a bit; but may not change sequence if next letters code for same thing [like near end] • TAC – UUA – UAA  TAC – UUA – AUA – A • Met – Leu – [stop]  Met – Leu – Ile –

12. Discuss • Name AND explain the three types of mutation by their CAUSE.

13. DNA Mutations • 4 classifications (1-2) – BY EFFECT • silent (sense) – has no effect on amino acid sequence • AGU (serine)  AGC (serine) • missense – codes for a different amino acid • AGU (serine)  AGA (arginine)

14. DNA Mutations • 4 classifications (4) – BY EFFECT • nonsense • forms premature “stop” codon • UAC (tyrosine)  UAG (stop)

15. Discuss • Name AND explain the three types of mutation by their EFFECT.

16. DNA Mutations • …ALSO AN EFFECT…BUT WANTED TO PUT AFTER • frameshift – changes the “reading frame” • caused by insertion/deletion THE DOG RAN OUT  THE OGR ANO UTTHE DOG RAN OUT  THE DOG RAF NOU T • insertions/deletions in groups of three may not change reading frame, but can change amino acids formed causing protein to not function properly.

17. Chromosomal Mutations • Recall: Chromosomes are wound DNA – when chromosomes are altered, we are altering large portions of the DNA message, even if there is only a small change to the chromosome.

18. Chromosomal Mutations • Occur during meiosis • 4 types: (1) • deletion – piece of chromosome is lost • may be lethal depending on which gene is lost

19. Chromosomal Mutations • Occur during meiosis • 4 types: (2) • duplication – piece of chromosome is duplicated • often harmless

20. Chromosomal Mutations • Occur during meiosis • 4 types: (3) • inversion – piece of chromosome is inverted/flipped • typically lethal, but in rare cases is advantageous

21. Chromosomal Mutations • Occur during meiosis • 4 types: (4) • translocation – piece of chromosome is moved to another part of the same chromosome or moved to its homologue • typically lethal

22. Discuss • Name AND explain the four types of chromosomal mutations.

23. Non-Disjunction • Non-disjunction – pairs of chromosomes don’t separate properly during meiosis [metaphase] • Metaphase I – ALL gametes affected

24. Non-Disjunction • Non-disjunction – pairs of chromosomes don’t separate properly during meiosis [metaphase] • Metaphase II – only half of gametes affected

25. Non-Disjunction • Non-disjunction – pairs of chromosomes don’t separate properly during meiosis [metaphase] • causes types of “monosomy” or “trisomy” • ex: Trisomy-21, Trisomy-X, Monosomy-X, Showing Trisomy

26. Discuss • Explain the phenomenon of non-disjunction.

27. Polyploidy • Polyploidy – multiples of entire chromosome set. • lethal in humans, common in plants • plants: causes larger cells, larger plants • Examples: • peanuts = 4n • sugar cane = 8n • coffee = 2n, 4n, 6n, 8n • wheat = 6n

28. Polyploidy