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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