Transcript Mutations - Somers Public School District

Mutations
What Are Mutations?
Changes in the
nucleotide sequence of
DNA (big or small)
May occur in somatic
cells (aren’t passed to
offspring)
May occur in gametes
(eggs & sperm) and be
passed to offspring
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 Mutations
Chromosome Mutations
May Involve:
Changing the
structure of a
chromosome
The loss or gain
of part of a
chromosome
Chromosome Mutations
Six types exist:
Deletion
Inversion
Translocation
Insertion
Duplication
Aneuploidy by
nondisjunction
Deletion
Due to breakage
A piece of a
chromosome is lost
Disorders due to
chromosome deletions:
Cri du Chat – deletion of short arm
of 5
1p36 Deletion Syndrome-deletion
of short arm of 1
Angleman Syndrome- deletion of
short arm of maternal 15
Prader-Willi syndrome- deletion of
short arm of paternal
15
Inversion
Chromosome segment
breaks off
Segment flips around
backwards
Segment reattaches
Disorders caused by
inversions:
If they are “balanced”
they cause no
phenotype
If they are
“unbalanced” they
usually are associated
with a deletion and
several effects
Duplication
Occurs when a
gene sequence is
repeated
Translocation
Involves two
chromosomes that
aren’t homologous
Part of one
chromosome is
transferred to
another chromosome
and swapped with a
region of that
chromosome
Translocation
Disorders caused by
translocations
 “Robertsonian” usually show
no phenotypes but often
problems during meiosis
leading to miscarriages in
developing fetus.
 Common to have
Robertsonian traslocation of
13 and 14.
 If translocation of long arm of
21 and long arm of 14-Down’s
 Some cancer cells have
translocations (leukemia,
sarcoma)
Insertion
• A piece of one
Chromosome gets
Inserted into
Another
Chromosome
• Effect depends
on what was
Inserted and wheree
Nondisjunction
Failure of chromosomes to
separate during meiosis
Causes gamete to have too many
or too few chromosomes
Disorders:
 Down Syndrome – three 21st chromosomes
 Turner Syndrome – single X chromosome
 Klinefelter’s Syndrome – XXY chromosomes
Some Aneuploid
Chromosomal Disorders
Patau Syndrome
Edward Syndrome
Klinfelter’s Syndrome
Turner Syndrome
Super Male Syndrome
Super Female
Syndrome
Down’s Syndrome
Normal Male
2n = 46
20
Normal Female
2n = 46
21
47, XY, +13
serious eye, brain,
circulatory defects
as well as cleft
palate. 1:5000 live
births. Children
rarely live more
than a few months.
Patau Syndrome
Cleft Palate
Edward Syndrome
almost every organ system affected
1:10,000 live births. Children with full
Trisomy 18 generally do not live more
than a few months.
Male, Trisomy 21 (Down’s)
2n = 47
28
Female Down’s Syndrome
2n = 47
29
Down’s Syndrome
Down’s Syndrome
Characteristics
•
•
•
•
•
•
•
•
One in 733 births
Slow cognitive ability and growth
Small chin
Round face
Almond shaped, often upslanting eyes
Heart defects
Gastric reflux disease
Thyroid problems
Klinefelter’s Syndrome
2n = 47
32
Kleinfelter’s Syndrome
Turner’s Syndrome
2n = 45
34
Turner’s syndrome
Chromosome Mutation
Animation