Transcript ppt

Mutations &
Genetic Disorders
Headings
Vocabulary
Important Information
Mutations
Mutation:
 Any mistake or change in the DNA sequence
Point mutation:
 Change in
one nitrogen
base in DNA
 Ex: albinism
Chromosomal Mutation:

Changes in
chromosome
structure
1) INVERSION:
 the order of genes on
a chromosome is
inverted
2) TRANSLOCATION:
•the movement of a
chromosome fragment to
a nonhomologus
chromosome
3. DELETION
 Loss of a few bases
 Loss of large regions
of a chromosome
4. DUPLICATION
 Duplication of a few
bases
 Duplication of large
regions of a
chromosome
Crossing Over
 Occurs
when
chromosomes
exchange genes.
 2 chromosomes
overlap.
 Some genes
cross over and
switch places
NONDISJUNCTION
Nondisjunction:
 chromosome pair fails
to separate properly
during meiosis
Monosomy:
 gamete has 1 less
chromosome than it
should
 45 chromosomes
is the result
 Ex: Turner syndrome

Missing a sex
chromosome
Trisomy:
Gamete has 1
more chromosome
than it should
Result is 47
chromosomes
Ex: Down’s
Syndrome
Extra
#21
chromosome
Methods of Detection
Chorion villi sampling:
•Take sample of the chorion
–(membrane surrounding
fetus)
•Chemical tests and Karyotyping performed
Ultrasound:

Sound waves are used to
generate an image of the
unborn child.
 Used to detect abnormalities of
limbs, organs, etc.
Amniocentesis:
• Fluid surrounding the fetus is drawn out by
needle
• Fetal cells are collected and grown in a lab.
• Chromosomes can be then Karyotyped
Autosomal Disorders
 Down’s
Syndrome (Trisomy 21)
 Patau’s
Syndrome (Trisomy 13)
 Edward’s
Syndrome (Trisomy 18)
Down’s Syndrome (DS)
 Excess
# 21 chromosome
 Prenatal testing can be done
 Result of chromosomal mutation
 1 in 900 people born with this
 Likelihood of having a child with DS
increases with advancing maternal age
 Symptoms: mental retardation, upward
slant to eyes, small mouth, abnormal ear
shape, decreased muscle tone
 No cure
Patau’s Syndrome &
Edward’s Syndrome
 Cardiac
abnormalities
 Very severe conditions
 Most affected infants
die during first few
weeks of life
Deletion Disorders
 Angelman
Syndrome
 Prader-Willi
Syndrome
Angelman Syndrome
 Inappropriate
laughter with
convulsions
 Poor
coordination
 Mental
retardation
Prader-Willi Syndrome
Extremely
floppy
Obesity (constantly
hungry)
Mild mental
retardation
Sex Chromosome Disorders
 Klinefelter’s
 Turner’s
 Fragile
Syndrome
Syndrome
X Syndrome
Klinefelter’s Syndrome

47, XXY
 1 in 1000 male live births
 Mild learning difficulties
 Taller than average with
long lower limbs
 Show mild enlargement of
breasts
 Infertile (absence of
sperm)

Treat with testosterone
Turner’s Syndrome
 45,
X
 Low incidence
 Look normal
 Ovarian failure
 Normal intelligence
 Short stature
 Estrogen therapy
Fragile X Syndrome
 Most
common inherited
cause of mental
retardation
 1 in 2000 males
 High forehead,
prominent jaw, autism
 Gap in X chromosome
Single Gene Disorders
 Cystic
Fibrosis
 Hemophilia
 Sickle
Cell Anemia
 Phenylketonuria
Cystic Fibrosis (CF)

Recessive disorder
 Mutation stops production of
protein in lung cells,
pancreas
 Thick mucus, bacterial
infections in lung
 “sweat test”
 Most common in
Caucasians (1 in 3300)
 Chest percussions, diet
supplements
 Shortened life expectancy
Hemophilia
 Sex-linked
 Failure
of blood to clot
 Rare in females
 Injections with clotting factors to stop
bleeding episodes
 $350,000 a year in treatment
Sickle Cell Anemia

Mutation in blood protein
 “sickle” shape to RBC
 Screening tests
 Most common in African-Americans
(1 in 375)
 Pain associated with blocked vessels, causes
anemia (fatigue)
 Common where
mosquito-borne
malaria is present
PKU

Mutation disrupts function of enzyme
 Leads to high phenylalanine levels in brain
(poisons)
 Mental retardation, epilepsy
 Screening newborns (heel prick)
 1 in 10,000 Caucasian births
 Extremely rare in African-Americans
 Look normal
 Need low-protein diet,
smelly formulas
Self Quiz:
Quick Check for Understanding

1. Which of the following is an X-linked
disorder?


b. heel prick
c. X-ray
A. testosterone injections
b. chest percussions
4. Turner’s Syndrome is


A. amniocentesis
3. How are CF patients treated?


c. Down syndrome
2. How is PKU tested for?


A. Angelman B. hemophilia
A. 45, X
b. 46, XX
c. 47, XXY
5. Patients with Klinefelter’s Syndrome are

A. all male
b. all female c. male or female