Download Genetics - University of Puget Sound

Genetics and
Prenatal Screening
Genetics
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Each human cell contains 46
chromosomes made up of DNA.
Short segments of DNA are called
“genes”
Dominant and Recessive Genes
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When one is “dominant” then that
expression “trumps” the recessive gene.
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Carriers?
Table 3.2- Dark Hair/Blond, Curly/Straight,
Dimples/no dimples, double-jointed/normal joints
Chromosome and Genelinked Abnormalities
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Chromosome Abnormalities
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Down syndrome- trisomy 21
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round face, flattened skull, extra skin over
the eyelids, protruding tongue, short
limbs, and motor and mental retardation.
1/1900 @ 20 years; 1/45 @ 42 years
Chromosome and Genelinked Abnormalities
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Chromosome Abnormalities
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Down syndrome- trisomy 21
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round face, flattened skull, extra skin over the
eyelids, protruding tongue, short limbs, and motor
and mental retardation.
1/1900 @ 20 years; 1/45 @ 42 years
Fragile X- Problem with the X-chromosome:
often breaks
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typically mental retardation
more frequent in males. Why?
1/250 females are carriers vs. 1/800 males
Chromosome and Genelinked Abnormalities
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Genetic Abnormalities
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PKU- Phenylketonuria- Cannot properly
metabolize the substance (phenylalanine).
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mental retardation and hyperactivity if untreated.
“Curable” -Nature/nurture
Sickle-cell anemia- Deforms the body’s red
blood cells
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cells die causing anemia
Early death if left untreated.- Penicillin
1/400 Af-Am babies born with
<1/10 Af-Am are carriers
1/5 Africans
Prenatal Screening
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Dangerous- Why get it?
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<3% of preg genetic abnormalities
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20% of infant deaths
Parents have family history of
disease? Is mom/dad carrier?
(Dominant”)
Does mother have any diseases?
CMV-Cytomegalovirus
Are parents carries of a recessive
sickle cell allele
Prenatal Screening
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Family History
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Blood relatives with disorders
History of previous miscarriages
Children with specific genetic
disorders
Members of at-risk group
Mother’s age and Father’s age
Behavior- Do parents use
drugs/alcohol
Prenatal detection
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HCG-Human Chorionic
Gonadotropin- Blood test- similar to
a typical pregnancy test
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Can determine an ectopic pregnancy
Sometimes combined with….
Prenatal Detection
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AFP- Alpha-fetoprotein- (also a Blood
test)
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looking for AFP being produced amniotic
fluid and mothers blood.
Done at 15-20 weeks
Can determine if child has Down Syndrome
(Decreased Levels)- though only in about
60% of cases
Can “help” determine neural tube defects
such as spina bifida (Increased levels)
Fetal distress
Prenatal Detection
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Ultrasound- Standard of Care
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Done at about 20-22 weeks
2-D image using sound waves
Considered low-risk as long as nonrepeated exposure- possible low birth
weight
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Doppler Ultrasound- 1 hour sessionColor- Can look for signs of preeclampsia, poor blood flow.
Other ultrasounds
• http://www.youtube.com/watch?v=uo
5gOWzgoaY
• 4-D ultrasound
Prenatal Detection
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Amniocentesis
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Done between 16th and 18th week though
used to be done at 20th-22nd week.
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Why the change????
Takes two weeks to month to get results.
Needle through stomach, uterine wall, and
amniotic sac, remove small amt of fluid
Avg. range=.3-.5%, but as high as 3-8%
fetal loss
Risk of loss is greater than risk of birth
defects in older moms
Can detect several hundred diff birth defects
(out of 4000)
Prenatal Detection
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CVS- Chorionic Villi Sampling
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Done at 10-12 weeks
Results take less than 10 days
Using ultrasound, take fetal cells from
the chorion (placenta)
between a 0.5% and 1% risk of
miscarriage
Slightly higher risk than amnio
Possible birth defects (1/3000)