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Advanced
Biology
Chapter 13
Genetic Disorders
• Autosomes – 22 perfectly
matched chromosomes.
• #s 1-22
• Sex Chromosomes –
pair
• XX = Female
• XY = Male
rd
23
• Monosomic – Lost one
copy of a chromosome
• Usually fatal, especially if
on an autosome
• Trisomic – Extra
chromosome
• 13, 15, 18 can have an extra
and survive for a short time
• 21, 22 can survive into
adulthood
• Down Syndrome –
Trisomy 21
st
• Extra copy of the 21
chromosome
• Primary Nondisjunction –
Failure of chromosomes to
separate during Meiosis
• Failure to separate is correlated
to age:
• >20 – 1:1700 births
• 20-30 – 1:1400
• 30-35 – 1:750
• 35-45 – 1:16
• Barr Body – One of the X
chromosomes is
inactivated
• Y Chromsome – Possesses
some active genes, contains
features associated with
maleness
• Contains 78 genes
NONDISJUNCTION IN SEX
CHROMOMSOMES
• Triple X syndrome - XXX
• One functional X, two Barr
Bodies
• Female is sterile but normal
in other respects
NONDISJUNCTION IN SEX
CHROMOMSOMES
• Klinefelter Syndrome – XXY
• Sterile Male
• Has many female characteristics
• May have diminished mental
capacity
• 1:500
NONDISJUNCTION IN SEX
CHROMOMSOMES
• Turner Syndrome – XO
• Sterile Female
• Short in stature, webbed neck
• Sex organs never fully mature
• Low mental abilities
• 1:5,000
NONDISJUNCTION IN SEX
CHROMOMSOMES
• Nonviable – OY
• Fails to develop
• Humans cannot survive
without the genes on the X
chromosome
• Multiple alleles – Some traits
possess multiple alleles for
that specific trait
• Blood types.
GENETIC DISORDERS
• Cystic Fibrosis
• Autosomal
• Occurs mainly in the white
population
• 1:20 carry the allele
• 1:1800 are homozygous recessive
GENETIC DISORDERS
• A malfunction in a channel
protein causes a thick mucus
to be produced in the lungs
• Can also affect ducts in the
pancreas
• Most affected individuals die in
their teens
GENETIC DISORDERS
• Sickle Cell Anemia
• Autosomal Recessive
• Occurs more frequently in
the black pop.
• 1:1600
GENETIC DISORDERS
• Hemoglobin is defective;
doesn’t carry enough
Oxygen
GENETIC DISORDERS
• Phenylketonuria (PKU)
• Autosomal recessive
• 1:15,000
GENETIC DISORDERS
• Inability to breakdown
phenylalanine (aa)
• Can be controlled by
nutrition
GENETIC DISORDERS
• Tay-Sachs Disease
• Autosomal Recessive
• 1:3600 if of Jewish decent
• 1:300,000 in U.S
GENETIC DISORDERS
• Affected individuals lack an
enzyme that breaks down
gangliosides in the brain
• These accumulate in the
lysosome and burst
• Resulting in the destruction of
brain cells
GENETIC DISORDERS
• Sex-linked recessive
• Inability of blood to clot
• Missing a clotting factor
GENETIC DISORDERS
•
•
•
•
Huntington’s Disease
DOMINANT
1:10,000
Gene gets turned on in middle
age
GENETIC DISORDERS
• Deterioration of brain cells
due to the inhibition of brain
cell metabolism
GENETIC DISORDERS
• High risk pregnancies
• Parents who are:
–Heterozygous for a disease
–Older
OR have a family history
GENETIC COUNSELING
• Ultrasound – position of fetus
• Amniocentesis
• Withdraw fluid containing fetal
cells
GENETIC COUNSELING
• Chorionic Villi Sampling
• Take a sample of placental
tissue
GENE THERAPY
• Gene Transfer Therapy
• 1st done in 1990
• 2 Girls had a rare blood disorder
due to a defective gene
• Scientists isolated working
copies of the gene
GENE THERAPY
• Introduced them into bone marrow
cells taken from each girl
• Gene modified bone marrow cells
were allowed to proliferate (make
more)
• Injected back into body
• Both girls healthy
GENE THERAPY
• Use of vectors (1995)
• Attach gene to a virus –
adenovirus (cold)
• Like a piggyback ride
• Tried it with mice and the cf
gene
GENE THERAPY
• Worked, tried it with humans
• Worked for awhile, but
eventually immune system
attacked virus
• Caused the loss of the good
gene
GENE THERAPY
• Problems with the vector:
–Adenovirus elicits a strong
immune response (everyone
has had a cold)
–Adenovirus can produced a
severe immune reaction and be
fatal
GENE THERAPY
Problems with the vector:
–Adenovirus inserts its DNA
into cell at a random location
causing mutations
GENE THERAPY
• Few years later, found new
vector
• Use Parovirus called AdenoAssociated Virus (AAV)
• Has only two genes and needs
the adenovirus to replicate
GENE THERAPY
• Scientists removed the two
genes and insert human genes
in their place to take them into
the cell
• Does not cause the problems
that the adenovirus did
GENE THERAPY
• In 1999, AAV cured anemia in
rhesus monkeys.
• Also cured dogs of retinal
degeneration
• In 2000 first human trial