Transcript CHANGES IN THE GENETIC CODE

CHANGES IN THE
GENETIC CODE
Ectrodactyly
What do they all have in common?
They’re all mutations!
MUTATIONS
a change in the DNA code
causes a different (sometimes wrong)
type of protein to be made
may or may not be good for the
organism
ALONG THE WAY
good changes occur
bad changes occur
changes that don’t matter either way
CHANGE IS NECESSARY
without changes we would all look alike
without changes we would not evolve
without changes we would not develop
immunities to disease
SO… Is change/variation a good
thing???
YES!
Causes of Variation
Crossing Over
Mutations
– Some happen randomly
– Some caused by Mutagens (agents that
cause mutations)
Nuclear Radiation
Ultraviolet Light
X Rays
http://learn.genetics.utah.edu/units/disorders/slooz
eworm/mutationbg.cfm
CROSSING OVER
occurs when homologous chromosomes
trade segments
occurs during Prophase I of Meiosis
entire gene is switched
involves the variation of a single trait
– gene for big ears exchanges with gene
for small ears
Advantages
variation of offspring from parents
allows for “good” changes
Better chance of passing on genes for
survival
3 TYPES OF MUTATIONS
Chromosomal mutations
Gene mutations
Somatic mutations
– these usually occur during mitosis and
involve a chromosomal mutation
– involved with body cells, not sex cells
– tumors are the result
Research your mutation
1. Answer these questions
– What does the name of the mutation mean?
– What happens to the chromosome?
– What is an example?
CHROMOSOMAL
MUTATIONS
NONDISJUNCTION
DELETION
INVERSION
DUPLICATION
TRANSLOCATION
INSERTION
NONDISJUNCTION
failure of homologous pairs to separate
during meiosis
correct number of chromosomes are not
present in the gamete
after fertilization, diploid number is not
restored
Examples
Trisomy 21(Down Syndrome)- 3 copies
of chromosome 21
Klinefelters Syndrome- XXY
Turner Syndrome- X
“Supermales” - XYY
DELETION
A SEGMENT OF A
CHROMOSOME IS
DELETED
Examples
Cri-du-chat syndrome- “cry of the cat”deletion of piece of chromosome #5
Angelman Syndrome- deletion of piece
of chromosome #15
Prader-Willi Syndrome- deletion of
piece of chromosome #15
INVERSION
A SEGMENT OF THE
CHROMOSOME IS
FLIPPED IN THE
OPPOSITE DIRECTION
DUPLICATION
A SEGMENT OF THE
CHROMOSOME IS COPIED
TWICE
TRANSLOCATION
SEGMENTS
FROM TWO
DIFFERENT
CHROMOSOMES
ARE SWITCHED
Example
Translocation Down Syndrome
Instead of being 3 separate copies of
chromosome 21, the extra copy is
actually attached to another
chromosome
INSERTION
A SEGMENT OF ONE CHROMOSOME IS
INSERTED INTO A DIFFERENT CHROMOSOME
GENE MUTATIONS
POINT MUTATIONS
FRAME SHIFT
– insertions
– deletions
INVERSIONS
LETS MUTATE!
Start with an original strand of DNA
GCC TTA CGT TTA CGA CTG TAC GTA
CGG AAT GCA AAT GCT GAC ATG CAT
A
B
C
D
AMINO ACIDS
lets assume this strand codes for a protein
POINT MUTATIONS
TTA CGT TTA CGA
AAT GCA AAT GCT
ORIGINAL
1 base is replaced with another base
B
TTA CTT TTA CGA
AAT GAA AAT GCT
E
MUTATION
Example
Sickle Cell Anemia- changing 1 base causes
mutation that codes for valine instead of
glutamate in the protein hemoglobin
Individuals produce different type of
hemoglobin
Red Blood Cells become sickle shaped and
don’t pass thru blood vessels as easily
Cells die sooner than normal
Individuals don’t get as much oxygen
http://www.montgomerycollege.edu/~wole
xik/Sickle%20Cell%20Anemia%20400x.jp
g
FRAME SHIFTS
TTA CGT TTA CGA
AAT GCA AAT GCT
A
B
C
D
TTA CGT TTA ACG A
AAT GCA AAT TGC T
A
B
C
F
TTA CGT TAC GA
AAT GCA ATG CT
A
B
G
ORIGINAL
INSERTION-base is
inserted
DELETION- base is
deleted
INVERSIONS
TTA CGT TTA CGA
AAT GCA AAT GCT
A
B
C
ORIGINAL
D
Codon is found in reverse order
TTA TGC TTA CGA
AAT ACG AAT GCT
A
H
C
D
INVERSION
Consequences
Sometimes mutations are bad and cause
for different proteins to be made
But- if you look at the amino acid chartseveral different codons code for the
same amino acids
Mutations can occur but wouldn’t be
noticed
Some mutations are masked by other
genes