Unit 4 – Lecture 4

MutationsGenetic Mutation – a change in the amount or

structure of genetic material of an organismMutations can be in DNA or can be

chromosomalMutations 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 replicatedproblems are typically noticed and

repaired by enzymes during growth typically mismatch in base pairingproblem in DNA problem in mRNA

problem in protein synthesis

Effects of MutationsALL known mutations are harmful overall

some are beneficial under certain circumstancesantibiotic 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 MutationsALL known mutations are harmful overall

some are beneficial under certain circumstancessickle-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 = 42-48 yrs old]

Effects of MutationsSmall changes:

may cause no change in the a.as formedmay cause a change in the a.as formedmay cause MASSIVE change in the

a.asformedLarge changes…are of course, typically

worse than small changes

Effects of MutationsCan cause cancers, genetic disordersMutations in cells:

in gametes – passed to the next generationin somatic cells – not passed on to next

generation

DNA Mutations3 types (1)

substitution – change of a single base from one kind to another [aka point mutation]ex: THE DOG RAN OUT THE FOG RAN

OUTmay or may not alter the amino acid

formed:CAU & CAC both code for HistidineCAA & CAG both code for Glutamine

DNA Mutations3 types (2)

deletion – a single base is deleted from the sequence

THE DOG RAN OUT THE OGR ANO UTchanges 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 – AAMet – Leu – [stop] Met – Phe –

DNA Mutations3 types (3)

insertion – a single base is added to the sequenceTHE 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 Mutations4 classifications (1-2)

silent – has no effect on amino acid sequenceAGU (serine) AGC (serine)

missense – codes for a different amino acidAGU (serine) AGA (arginine)

DNA Mutations4 classifications (3-4)

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.

DNA Mutations4 classifications (4)

nonsenseforms premature “stop” codonUAC (tyrosine) UAG (stop)

Chromosomal MutationsRecall: 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 MutationsOccur during meiosis4 types: (1)

deletion – piece of chromosome is lostmay be lethal depending on which gene is

lost

Chromosomal MutationsOccur during meiosis4 types: (2)

duplication – piece of chromosome is duplicatedoften harmless

Chromosomal MutationsOccur during meiosis4 types: (3)

inversion – piece of chromosome is inverted/flippedtypically lethal, but in rare cases is

advantageous

Chromosomal MutationsOccur during meiosis4 types: (4)

translocation – piece of chromosome is moved to another part of the same chromosome or moved to its homologuetypically lethal

Non-DisjunctionNon-disjunction – pairs of chromosomes don’t

separate properly during meiosis [metaphase]Metaphase I – ALL gametes affected

Non-DisjunctionNon-disjunction – pairs of chromosomes don’t

separate properly during meiosis [metaphase]Metaphase II – only half of gametes

affected

Non-Disjunction

PolyploidyPolyploidy – multiples of entire chromosome

set.lethal in humans, common in plants

plants: causes larger cells, larger plantsExamples:

peanuts = 4nsugar cane = 8ncoffee = 2n, 4n, 6n, 8nwheat = 6n

Polyploidy