Transcript GENETIC MUTATIONS - Manning's Science

Mutations:
Changing DNA
SBI4U Biology
Mutation:
A change in the DNA sequence that is inherited as
the DNA is transmitted through cell division.
Changes in number or structure of chromosomes
 Spontaneous
 Induced
 Mutagens = UV, X Rays, other radiation;
chemicals; heavy metals

Categorising mutations
1. By effect on structure
2. By consequences on resulting proteins
1. Mutations by effect on structure
a) Point mutations
 Mutations that occur to a specific base pair in
the genome.
b) Chromosomal mutations
 Mutations that involve large segments of DNA.
Point mutations
 Substitution: One base pair is replaced with another
Point mutations (cont`d)
 Deletion: One or more base pairs is eliminated from
the DNA sequence
Point mutations (cont`d)
 Insertion: One or more base pairs is inserted into the
DNA sequence
Frameshift mutations
 Deletions and insertions of 1-2 base pairs will result in
a shift in the reading frame.
 “frameshift mutations”
 Deleting or inserting 3 base pairs is not considered a
frameshift mutation... why??
Chromosomal mutations
Large scale changes to chromosomes
 Inversion :
The reversal of a segment of DNA within a
chromosome.
 Results from breaking and rejoining (upside down)
Chromosomal mutations (cont`d)
 Translocation:
A fragment of DNA
moves from one
part of the genome
to another.
 Can result in a
“fusion protein”
Chromosomal mutations (cont`d)
 Gene duplication:
Duplication of a coding
region of DNA along a
chromosome
 Results from crossing over
of misaligned homologues
during meiosis I
Chromosomal mutations (cont`d)
 Deletion:
Part of a chromosome is
deleted and becomes
“missing”
Chromosomal mutations (cont`d)
 Insertion:
The complement of deletion. Part of another
chromosome is inserted.
Gross
Chromosomal
Gross Chromosomal




Aneuploidy = incorrect number of
chromosomes
Trisomy = extra chromosome (2n +1)
Monosomy = missing chromosome (2n -1)
Triploid = 3n, Tetraploid = 4n
Trisomy & Monosomy
2. Mutations by consequence on
resulting protein
a) Silent mutations
b) Missense mutations
c) Nonsense mutations
Silent mutations
 Does not result in a change in amino acid sequence
no phenotypic change; no effect on the cell
How?
 May occur within
an intron
 Redundancy of
genetic code
ACA and ACU are both
codons for threonine
Missense mutations
 Results in a change to a codon
The wrong amino acid is incorporated
Does not necessarily drastically alter protein function
Checkpoint:
Can you classify
this mutation
by its effect on
structure?
Nonsense mutations
 A codon is converted to a stop codon
truncated protein is produced
Checkpoint:
Can you classify
this mutation
by its effect on
structure?
Mutation Examples:
I LOVE HER SO MUCH I COULD MARRY HER.
Silent:
I LOVE HER SO MUCH I COULD WED HER.
Missense:
I LOVE HER SO MUCH I COULD PUNCH HER.
Mutation Examples:
I LOVE HER SO MUCH I COULD MARRY HER.
Chain Termination:
I LOVE HER SO MUCH I COULD.
Nonsense:
I LOVE HER SO MUCH I COULD MARY HERE THIRST
PINK UTAH MONGOOSE LABEL WINE FLIRT LAVA
LAMP TOOL BARGE MAPLE NOSE HAIR RITZ
CRACKER CONSPIRACY GONG SHOPPING SPREE
WIT’S END NEVADA WONDERFUL SQUID RICE
KANGAROO CELEBRATE WART…
Mutation Examples:
I LOVE HER SO MUCH I COULD MARRY HER.
Deletion Frameshift:
I LOVH ERS OM UCHI C OULDM ARRYH ER
Insertion Framshift:
I LOXV EHE RS OMUC H ICOUL DMARR YHE R
Consolidation
substitution
Point
mutations
insertion
Effect on
structure
Chromosomal
mutations
MUTATIONS
deletion
inversion
translocation
Effect on
protein
Silent
duplication
Missense
deletion
Nonsense
insertion
Causes of mutations
Innate
 Spontaneous: Due to errors in replication
Environmental
 Exposure to mutagenic agents
 UV radiation, X rays, chemicals