Unit 4 – Lecture 4

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

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

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

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

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

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

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.

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 = phenylalanine UUA = leucine

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 –

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 –

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

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)

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

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

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 UT THE 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.

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.

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

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

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

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

Discuss Name AND explain the four types of chromosomal mutations.

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

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

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

Discuss Explain the phenomenon of non-disjunction.

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

Polyploidy