Transcript Genetic Screening

Gene Pool
Total number of genes of every
individual in an interbreeding population
A large gene pool:

Means a high genetic
diversity

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
A lot of good and
bad traits within
one population
Increase in the fitness
of the population
Increase in the
survival of the that
population
A small gene pool:


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Means a low genetic
diversity
Decrease in the fitness of
the population
Increases in the chance
of extinction
Survival of the fittest
The fittest
organisms within a
species survives the
best and are then
able to pass their
“good genes” on to
future generations
allowing the species
to evolve in a
positive way.
Evolution
-The primary mechanism for change over
time is NATURAL SELECTION
-Variation exists within all populations of
organisms. This occurs partly because
random mutations cause changes in the
genome of an individual organism, and these
mutations can be passed to offspring.
-Individuals with certain variants of the trait
may survive and reproduce more than
individuals with other variants. Therefore the
population evolves.
Natural selection doesn't lead to the development of
a new species.
In most cases, the process simply allows a species to
better adapt to its environment by changing the
genetic make up from one generation to the next.
If a species lacks a certain trait that will allow it to
survive, there are two options:


Either the species dies out OR
It develops the missing trait and survives
Natural selection
Darwin’s
finches of
the
Galapagos
islands
Selective Breeding
Selective breeding
(also called artificial
selection) is the
process of breeding
plants and animals for
particular traits.
Evidence of evolution
Fossil Record
Homologous structures
Same structures
but different
functions.

Vestigial structures
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Serves NO function
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Were useful to ancestors…
but not useful for modern organism
Tailbone
Comparative Embryology
Macromolecules:

Proteins
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Blood antigens
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Human and Frog differ by 67 Amino Acids
DNA
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Chimpanzees 98.7% exact to Humans
The driving force behind
evolution are mutations
Ways to increase the gene pool and
increase variation in offspring
1. Crossing over:
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Like pairs of chromosomes/homologous
chromosomes touch and segments of the
chromosomes switch places, mixing up what
genes a sperm or egg contain.
2. Mutations:
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Changes in the DNA sequence
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Can be bad and cause a genetic disorder
OR
Can be good and produce a new trait that makes the
organism more fit
 -main cause of evolution
Types:
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1. Germ mutations
 Occurs in sperm or egg and is passed on to the
offspring

2. Somatic mutations
 Occurs in the body cells, not passed on to
offspring
3. Gene mutation
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A change in a nucleotide results in a different
DNA sequence
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Silent
Missense
Nonsense
4. Chromosomal mutations
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1. Deletion
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Change in the structure of a chromosome OR a
loss or addition of an entire chromosome
Loss of a piece of a chromosome due to
chromosomal breakage
2. Inversion

A chromosomal segment breaks off and then
reattaches in a reversed orientation to the
same chromosome

3. Translocation
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Chromosome piece breaks off and reattaches to
another, entirely different chromosome

4. Nondisjunction
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Improper division of chromosomes during meiosis
Creating sex cells with too many chromosomes
Sperm or egg with 47 chromosomes
Example: Trisomy 21 or Down Syndrome
Or
Creating sex cells with too few chromosomes
Sperm and egg with 45 chromosomes
Example: Monosomy X or Turners Syndrome
Genetic Screening
Detecting Genetic Disorders
Genetic disorders are not rare, in fact, more than
20% of children admitted to the hospital are there
because of genetic disorders or birth defects.
Only four percent of the
children in the United
States are severely limited
or multiply handicapped
because of genetic disorders
or birth defects, yet, these
children account for 25% of
all pediatric hospital care.
Genetic Screening
Goal is to identify people with
genetic disorders and those who
have the potential of passing a
disorder on to an offspring.
What types of Genetic
Screening take place?
The three types of genetic screening are:
Pre-natal – which is done before birth.
 Newborn – this is done as close to the birth of
the baby as possible.
 Carrier – this is done much later in life when a
person is considering having kids.

If screening reveals problems are likely, further testing would be
required in order to make a positive diagnosis.
Pre-natal Genetic
Screening
Why identify fetuses
with defects?
Follow-up tests can give some information
on the severity of the defect
Allows time to prepare for a potentially highrisk delivery and provides a better chance for
the babies well-being
Provides a chance for emotional and
practical preparation on the parents behalf
And sadly allow for the option of termination
Prenatal Screening
Used in the
identification of an
individual with a
genetic disorder
before birth, which is
known as prenataldiagnosis.
Blood Serum Assay
A simple blood test during the early part of
the pregnancy can reveal a great amount of
information at no risk to the embryo.
Alpha-Feto-Protein
(AFP)
AFP is a protein made by the
fetus.
It is first made in the yolk sac
and then in the fetal liver after it
develops and passes into the
mother’s blood through the
placenta.
AFP is the major serum protein
of the fetus
Determining Defects
from AFP levels
AFP levels can be
measured from the
mothers blood because
of the exchange of
nutrients through the
placenta. Between 16
an 18 weeks of
gestation is the ideal
time for testing because
AFP levels are easily
measured.
Low level AFP results
Abnormally low levels
of AFP can indicate
non-pregnancies and
chromosomal
disorders such as
Down Syndrome
(Trisomy 21)
Developmental Patterns in
Down Syndrome
Classic features of a
Trisomy 21 person
Those born with Down
Syndrome, as they
become older, exhibit
classic features such as:
Extra
folds of skin
around the eyes
Flat
mid-face
Smaller,
low set
ears
Low I.Q.’s
Decreased
tone
muscle
High level AFP results
Abnormally high levels of
AFP can indicate that the
fetus has a neural tube
defect, a ventral wall defect
or some other type of
abnormality.
Warning….. The next
slide may contain a
photo that you may not
wish to view.
Neural Tube Defects
Open Spina Bifida
is an abnormality in the
development of the spinal cord
with the vertebral bones and
back failing to close over the
malformed spinal cord.
The severity of the symptoms
depends on the location of the
defect and the presence of other
abnormalities
In general, the closer the lesion is
to the head, the more severe the
problems will be…….
.
Warning….. The next
slide may contain a
photo that you may not
wish to view.
The most severe form of
a neural tube defect is
Anencephaly.
Anencephaly is
the failure of
the brain to
develop
correctly.
These infants
do not survive.
Warning….. The next
slide may contain a
photo that you may not
wish to view.
Ventral Wall Defects
are defects in the closure of the abdominal wall of the
fetal body. These are often associated with the
malformation of the abdominal organs.
The stillborn child has
Omphalocoel
which is a form of a
ventral wall defect that
results in a defect
where the abdominal
organs are in a sack
outside the body
cavity. The severity of
these types of defects
vary and some can be
surgically repaired
where as others are
fetal.
Warning….. The next
slide may contain a
photo that you may not
wish to view.
AFP testing will identify:
100% of pregnancies with
anencephaly
80% of pregnancies with spina
bifida
20% of pregnancies with Down
Syndrome
Many with ventral wall defects
And many high risk
pregnancies
Ultrasound
Examinations
Another useful prenatal
diagnostic technique is the
ultrasound. This is the use
of high frequency waves to
produce an image called a
sonogram. Not only is this a
useful test by itself but it can
also be used to confirm
problems suspected as a
result of other tests. This
test poses no threat to the
developing fetus.
Typical 28 week
sonogram
More current forms of a
sonogram.
Amniocentesis
is a useful prenatla diagnostic technique which
examines amniotic fluid or cells shed by the fetus into
this fluid.
Hurts no more than donating
blood…..Or so they say!
The amniotic fluid is
obtained by inserting a
needle into the
abdomen and amniotic
cavity. This procedure
can be done during the
16-18 week of
pregnancy. Results
take a few weeks to
obtain.
Fetal skin cells are examined for
cells in metaphase of mitosis.
A karyotype is then prepared so the
actual chromosomes of the fetus can
be examined.
Trisomy 21
Trisomy 18/Edwards
Syndrome
Babies with Trisomy
18 have neurological
abnormalities, faunlike ears, clenched
posture and hands and
rocker-bottom feet.
90% of the babies with
Trisomy 18 die before
2 months of age.
50% die by the age of 2 months
10-15% live to 18 months
Warning….. The next
slide may contain a
photo that you may not
wish to view.
Trisomy 13 / Patau’s Syndrome
Turner’s Syndrome
Klinefelter’s Syndrome
Chorionic villus biopsy is a prenatal diagnostic
technique where a small piece of the fetal chorion is
removed for testing. These cells can be used to
prepare a karyotype, for biochemical test or for
DNA assays. This technique can be performed
between 9-10 weeks of pregnancy and results
obtained within a few days.
Fetoscopy
is another prenatal diagnostic technique which uses a
fiber optic instrument, an endoscope. The endoscope is
passed into the uterus, and a small area of the fetus is
viewed. The endoscope can be used to aid in an “in
vitro” operation or used to obtain blood from the
umbilical cord.
NEWBORN
SCREENING
Another type of
genetic screening is
done shortly after
birth. This testing is
known as newborn
screening. Newborn
screening is done
on every child born
in a hospital within
the United States.
Red…5 or fewer
Yellow…6 to 8
Green…9 test
A sample of blood is drawn from the
baby’s heel soon after it has consumed it
first meal of breast milk or formula.
Newborn screening is testing for
metabolic disorders.
This sample of blood is
placed on filter paper,
given a specific code for
identification reasons and
sent to the State Health
Department for testing.
Testing Procedure
The actual test is
done on discs that
are punches four at
a time by the
machine pictured
here.
Continuing the testing
The discs are separated
and four different tests
are run.
The bacteria in the tray
can only be grown by
high concentrations of
amino acids that are
found in the blood of
some babies with
certain metabolic
disorders.
The Test Results
Present on the test are
frosted areas around
the discs that show the
presence of specific
metabolic products
which would only be
present in the blood of
sick and diseased
babies.
All are forms of “MISSENSE”
gene mutations
Metabolic disorders tested
for in Pennsylvania include:
PKU
Galactosemia
Maple Syrup Urine Disease
Tay Sachs
PKU: Phenylketonuria
People with PKU cannot metabolize phenylalanine into tyrosine.
Tyrosine is needed for normal growth and development
including neurological receptors and pigments. If detected
early, PKU can be controlled through a special diet. These
special diets include foods which contain a limited amount of
phenylalanine. Regular milk and formula are very high in
phenylalanine.
Tested and provided
with a ow
Phenylalanine diet.
Not tested at birth
and feed normal
diet of formula.
Children with PKU
grow up normally and
eventually think
about having their
own children.
Females with PKU
must go on a strict
diet whenever they
contemplate having
children of their own.
Maple Syrup Urine
Disease
Carrier
Screening
Recessive Pedigrees
A person with one normal
gene and one abnormal
gene of a disorder is a
carrier of that disorder.
A person may carry a
disorder and still be healthy.
When both parents are
carriers of the same disorder
there is a 25% chance that
the child will be affected,
25% that they’ll be
unaffected and 50% that
they will be carriers.
Meeting With the Doctor
Testing is available to
couples contemplating
parenthood.
If both parents have
been identified as
carriers, and the couple,
therefore, is at risk of
having a child with a
genetic defect, they can
be offered genetic
counseling.
Tay Sachs Disease
is common among people with Middle European
Jewish ancestry.
People of this descent have a 1:20 chance of being a
carrier for this disorder.
Children with Tay Sachs appear normal at birth but they lack the enzyme,
hexosaminidase, which is necessary to break down some complicated fats in the
nervous system. This fat build up and cause progressive damage to the central
nervous system.
Symptoms first appear between 4 to 8 months of age. The child
becomes blind, develops seizures, and becomes progressively less
responsive to the environment and die by the age of 3 to 4 years of
age.
Cherry Red Eye Spot
Sickle Cell Anemia
Sickle cell anemia is a disease characterized by an abnormal
hemoglobin. This abnormal hemoglobin causes the red blood
cells to be made in an abnormal sickle shape. 5% of children
with sickle cell die before age two. 10% die by the age of 10.
Codominate Trait
A person who is heterozygous for sickle cell have 50% of
their blood cells normal shape and 50% of their blood cells
sickle shape.
Albinism
Dominant Diseases
Dwarfism/Achondroplasis
Huntington’s Disease
Huntington's disease (HD) results
from genetically programmed
degeneration of brain cells, called
neurons, in certain areas of the
brain. This degeneration causes
uncontrolled movements, loss of
intellectual faculties, and emotional
disturbance.
Marfan’s Syndrome
Sex Linked Diseases
Hemophilia
Duchenne Muscular
Dystrophy
What are the options for
carrier couples?
1. Choose other mates
2. Not have children
3. Adopt
4. Take the risk of having an affected child
5. Use artificial insemination by donor, egg
donor or surrogate mother, etc…
The End