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: bacteria are immune to harm from antibiotics [good], but causes them to be less efficient at many other cellular processes [competing for resources, rate of reproduction]

Effects of Mutations ALL known mutations are harmful overall some are beneficial under certain circumstances sickle-cell anemia: humans with this disease are less likely to get malaria [good], but cell shape obstructs capillaries & blood flow leading to pain or organ damage [typical life span = yrs 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

DNA Mutations 3 types (1) 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

DNA Mutations 3 types (2) 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) 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 –

DNA Mutations 4 classifications (1-2) silent – 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 (3-4) 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.

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

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

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

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