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Genetic Disorders
AP Biology
Detecting Genetic Disorders
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Amniocentesis
Chorionic villus sampling
Karyotype
Sequential Screen (Quad/Triple Screen)
Blood Test
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Amniocentesis A technique for
determining genetic abnormalities in a
fetus by the presence of certain
chemicals or defective fetal cells in the
amniotic fluid, obtained by aspiration
from a needle inserted into the uterus.
CVS –sample of embryonic cells taken
for chorionic villus (placenta) can be
done earlier than amniocentesis and
results yielded sooner
Karyotype
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A method of
organizing the
chromosomes of
a cell in relation
to number, size,
and type. Taken
during
METAPHASE of
Mitosis.
Karyotype
Normal Male
Normal Female
NON-DISJUNCTION
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Chromosomes fail to separate
properly - can occur during
meiosis I (all cells affected) or
meiosis II (half cells affected)
Aneuploidy - having an abnormal
chromosome number
Trisomic/TRISOMY - having 3
chromosomes 2n+1
Monosomic - having 1
chromosome 2n-1
Polyploidy - having move than 2
sets of chromosomes
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Triploidy - (3n)
Tetraploidy - (4n) common in
plants – usually lethal in animals
and humans
Nondisjunction Disorders
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Down’s Syndrome - Trisomy 21
Edward’s Syndrome - Trisomy 18
Patau’s Syndrome - Trisomy 13
Turner’s Syndrome - X0
Klinefelter’s Syndrome - XXY
Super Male - XYY
Super Female - XXX
Down’s Syndrome
Characteristic facial features, low
mental ability, stocky build,
sometimes heart defects.
Extra copy of chromosome #21 –
Trisomy 21
Edward’s Syndrome
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Trisomy 18
Motor and mental retardation
Congenital heart disease
Often dies in infancy
Patau’s Syndrome
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Trisomy 13
Physical abnormalities – cleft palate,
polydactaly, microcephaly
Turner Syndrome
• XO
•Female missing one X
chromosome
• short stature
• wide neck with extra
skin folds
• underdevelopment of
sex characteristics –
may lead to sterility
• non-disjunction of sex
chromosomes
Klinefelter’s Syndrome XXY
• XXY
• male with extra X
chromosome
•poor sexual
development, may be
sterile
• subnormal mental
ability
• other forms are
XXYY, XXXY, XXXXY
(additional X’s
increase the severity
of phenotypes and
mental retardation)
Super Male
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XYY Jacob’s Syndrome
Male with extra Y chromosome
Very tall, can show violent behavior
Prone to acne
Impaired fertility
Mentally normal
Chromosomal Abnormalities
Short Arm of # 5
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Cri – du- chat
Cat-like cry
Severe physical
and mental
abnormalities
nonlethal
Gene Mutations
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Point mutations
 Changes in 1 or a few base
pairs in a single gene
 Substitutions
Base-pair insertions or
deletions: - Can result in a
frameshift mutation alters
the ‘reading frame’ of
triplets
THE FAT CAT ATE …
THF ATC ATA TE….
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Point
Gene Abnormalities
Substitution
Silent – no change in aa
Nonsense – STOP CODON
Missense – change in aa
THE FAT CAT ATE THE RAT  TOE FAT CAT ATE THE RAT
 *Insertion/Addition
 *Deletion
*May result in a Frame-Shift Mutation
THE FAT CAT ATE THE RAT  THF ATC ATA TET HER AT
(ENTIRE MESSAGE SHIFTS)
Transposons (jumping genes) – transfer of a gene from one locus
to another on a chromosome – may unactivate relocated gene –
which may produce a point mutation and could result in the
elimination of a vital metabolic pathway
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Sickle Cell Anemia
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Abnormal hemoglobin
1 aa substitution
causes abnormality
(point mutation)
Codominance
(carrier)
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Low oxygen RBC will
become crescent
shape
Inherited Genetic Disorders
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Autosomal Dominant
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Autosomal Recessive
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Inherit one allele
Must inherit two recessive alleles, one from each
parent. Parent’s are usually CARRIERS of the
disorder
Sex-Linked Disorders
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Usually recessive, inherited on X-chromosome
More common in males
Autosomal Dominant
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Huntington’s Disease
Marfan Syndrome
Achondroplasia
Huntington’s Disease
Autosomal Dominant Disorder
(lethal)
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CNS problem
Dementia
Impaired memory
Asymptomatic until
later in life (40)
Marfan Syndrome
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Autosomal Dominant
Connective tissue defect
Tall, thin, long arms and legs
Enlarged aorta
Abe Lincoln did NOT have
Marfan Syndrome
Achondroplasia
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Autosomal Dominant
Defects in growth of long bones
Form of dwarfism
Short arms and legs but torso of normal
size, large head compared to body
Autosomal Recessive
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PKU
Albinism
Tay Sachs
Cystic Fibrosis
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PKU
Phenylketonuria
Autosomal Recessive
Lack enzyme to
convert phenylalanine
to tyrosine
Buildup of
phenylalanine can
cause retardation
Test babies at birth
Special diet for
phenylketonurics
Albinism
• Lack of
pigmentation in
skin, hair, eyes
• Inability to make
melanin
• Autosomal
recessive
Tay-Sachs
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Autosomal recessive
Degeneration of nervous
system
No enzyme to break down lipids
in brain cells, so they swell and
die (death by age 5) - Lethal
High incidence in Ashkenazie
Jews
Blood test available to
potential parents
Cystic Fibrosis
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Cystic Fibrosis, incurable
hereditary disorder that causes
the body to secrete an
abnormally thick, sticky mucus
that clogs the pancreas and the
lungs, leading to problems with
breathing and digestion,
infection, and ultimately, death.
Common among Caucasians
One of the most common fatal
genetic disorders in the United
States
Lethal
Autosomal recessive, caused by
missing 3 bases/1 aa
(phenylalanine) protein does not
fold correctly
Sex-Linked Traits
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Gene loci on a sex-linked chromosome
Genes for many sex-linked traits, unrelated
to gender, are found on the X chromosome
Follow Mendelian Laws of Inheritance
May be either dominant or recessive
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Hemophilia
Duchenne Muscular Dystrophy
Colorblindness
Hemophilia
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Sex-linked recessive disorder
Lack of protein necessary for normal blood clotting
Duchenne Muscular Dystrophy
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Sex-linked recessive disorder
Absence of muscle protein dystrophin
Progressive muscle deterioration and loss of
coordination – most die by age of 20
Colorblindness