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MUTATIONS
Mutations

Changes to DNA are called mutations
change the DNA
DNA
 changes the mRNA
 may change protein
mRNA
 may change trait

protein
trait
TACGCACATTTACGTACG
AUGCGUGUAAAUGCAUGC
aa aa aa aa aa aa aa
What Causes Mutations?

There are two ways in which DNA can become
mutated:
 Mutations
 Parent
can be inherited.
to child
 Mutations
can be acquired.
 Environmental
damage
 Mistakes when DNA is copied
Are Mutations Helpful or Harmful?
Mutations happen
regularly
 Almost all mutations are
neutral
 Chemicals & UV radiation
cause mutations
 Many mutations are
repaired by enzymes

Are Mutations Helpful or Harmful?
Some type of skin
cancers and leukemia
result from somatic
mutations
 Some mutations may
improve an
organism’s survival
(beneficial)

Types of Chromosomal
Mutations
Chromosome Mutations

May Involve:
 Changing the
structure of a
chromosome
 Changing
number
the
Chromosome Mutations

Five types exist:
Deletion
Inversion
Duplication
Translocation
Nondisjunction
Deletion
Due to breakage
 A piece of a
chromosome is lost

ABCD-EFGH  ABCD-EF
Inversion
Chromosome segment
breaks off
 Segment flips around
backwards
 Segment reattaches

ABCD-EFGH  ABDC-EFGH
Duplication

Occurs when a gene
sequence is repeated
ABCD-EFGH  ABCDBCD-EFGH
Translocation
Involves two
chromosomes that
aren’t homologous
 Part of one chromosome
is transferred to another
chromosomes

ABCD-EFGH
WXY-Z  ABCD-EF WXY-ZGH
Translocation
Nondisjunction
Failure of chromosomes to separate
during meiosis
 Causes gamete to have too many or too
few chromosomes
 Disorders:

Syndrome – three 21st chromosomes
 Turner Syndrome – single X chromosome
 Klinefelter’s Syndrome – XXY chromosomes
 Down
Chromosome Mutation
Animation
Chromosome Mutations

Down Syndrome




Chromosome 21 does not
separate correctly. Trisomy
21
They have 47 chromosomes
in stead of 46.
Children with Down
Syndrome develop slower,
may have heart and stomach
illnesses and vary greatly in
their degree of intelligence.
Similar facial features
Chromosome Mutations

Cri-du-chat
of material on 5th
chromosome
 Characterized by the cat-like cry
made by cri-du-chat babies
 Varied levels of mental handicaps
 Deletion
Sex Chromosome Abnormalities

Klinefelter’s Syndrome
XXY, XXXY
 Male
 Sterility
 Small testicles
 Breast enlargement

Sex Chromosome Abnormalities

XYY Syndrome
Normal male traits
 Often tall and thin
 Associated with antisocial and behavioral problems*

Sex Chromosome Mutations

Turner’s Syndrome
X
 Female
 sex organs don't mature
at adolescence
 sterility
 short stature

Sex Chromosome Mutations

XXX
 Trisomy
X
 Female
 Little
or no visible differences
 tall stature
 learning disabilities
 limited fertility
KARYOTYPE
ANALYSIS

Karyotype
 Pictures
of paired
human chromosomes
arranged by size,
used to identify
abnormalities in
fetuses
 Cells from an amniotic
fluid sample are
cultured, stained &
photographed

1) Autosomes

all the chromosomes except
the sex chromosomes (in
humans, there are 22 pair)
2) Sex chromosomes

The sex-determining
chromosomes,
X&Y
the
Normal Male
2n = 46
28
Normal Female
2n = 46
29
Male, Trisomy 21 (Down’s)
2n = 47
30
Female Down’s Syndrome
2n = 47
31
Klinefelter’s Syndrome
2n = 47
32
Turner’s Syndrome
2n = 45
33