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Genetic Mutations &
Pedigrees
Genetic Mutations & Pedigrees
Alleles that code for defective proteins
can cause mutations & even deadly
disorders, which are passed on to us as
inherited traits.
Mutations can Cause Disorders
Sickle Cell Anemia:
Is caused by a mutated allele that
produces a defective form of a blood
protein called hemoglobin.
Hemoglobin is found inside our red
blood cells & is important because it
carries oxygen throughout the body.
Sickle Cell Anemia
This disease causes
red blood cells to
bend into a sickle
shape.
Sickle-shaped cells
burst easily & do not
function in carrying
oxygen very well.
Sickle Cell Anemia
For most sickle cell anemia is
considered harmful, but for some it
is beneficial.
The recessive allele responsible for
bending cells into a sickle shape
helps protect some individuals in
Africa and other countries from
contracting another disease called
malaria, a disease caused by
parasitic protists that invade red
blood cells & is carried by
mosquitoes.
Sickle Cell Anemia
People who are
heterozygous for
sickle cell anemia
have a mix of
normal red blood
cells and sickleshaped cells.
Sickle Cell Anemia
Sickle-shaped cells can’t be invaded by
parasites & normal red blood cells
provide enough oxygen for all body
tissues, so a person with sickle cell
anemia has the benefit of normal blood
cells to give oxygen & sickle cells, which
parasitic protists can’t invade.
Sickle Cell Anemia
People who are homozygous recessive
do not have this protection from malaria
and all of their red blood cells are
sickle-shaped due to the defective
protein hemoglobin.
Hemophilia
Hemophilia is a condition that impairs
the blood’s ability to clot.
Two of the genes that code for proteins
that cause this condition are found on
only on the X chromosome.
Because of this, males have an
increased risk of inheriting this disorder
because it is a sex-linked trait.
Chromosomes & Mutations
Each of our 46 chromosomes contain
thousands of genes that play an
important role in determining how our
bodies grow and function.
All genes must be present in order for
our bodies to function properly. Think
about it… would a car drive without an
engine, transmission or wheels?
Chromosomes & Mutations
In most cases, humans that are missing
even one chromosome do not survive
embryonic development and are never
born.
When a chromosome is missing, this
condition is called a monosomy.
When there is a chromosome has an extra
copy this condition is called a trisomy.
Chromosomes & Mutations
Monosomies, trisomies and other
genetic abnormalities can be
detected by looking at a karyotype
of a person’s chromosomes.
Chromosomes & Mutations
A karyotype is
a picture of
each pair of
chromosomes
in a cell.
Chromosomes & Mutations
Down’s syndrome
(also known as
Trisomy 21) is a
genetic deviation that
results in short size, a
round face & varying
degrees of mental
retardation. Why do
you think this occurs?
Chromosomes & Mutations
What events cause an extra copy of a
chromosome to occur?
When a cell divides normally each
chromosome & its homologue separate
in a process called disjunction.
Chromosomes & Mutations
When normal
disjunction (separation
of chromosomes) does
not occur
nondisjunction results
so that one of the new
cells ends up getting
both chromosomes of
the pair and the other
cell gets none.
Chromosomes & Mutations
Prenatal testing can be performed on a
pregnant woman to detect genetic
abnormalities:
1. Chorionic villi sampling
2. Amniocentesis
Prenatal Testing
Chorionic villi sampling- performed at 810 weeks.
A sample is taken from the villi that extend
down into the mother’s uterus.
The villi contain the same genetic information
as the fetus so the cells can be used to
construct a karyotype to detect genetic
abnormalities in the fetus.
Prenatal Testing
Prenatal Testing
Amniocentesisperformed at 14-16
weeks
A sample of amniotic
fluid is taken from the
sac surrounding the
fetus which contains
fetal cells, which are
used to make a
karyotype.
Genetic Mutations
While rare, changes in an organism’s
chromosome structure can occur. Some
changes can cause mutations in the
genes like these:
1. Deletions
2. Duplications
3. Inversion
4. Translocation
DELETIONS
This mutation that occurs when a fragment
of a cell breaks off as the cell divides.
DUPLICATION
A mutation that
occurs when a
chromosome
contains an extra
segment of DNA.
INVERSION
A mutation that occurs when a
chromosome fragment re-joins its
original chromosome, but its
nucleotides are reversed.
TRANSLOCATION
A mutation that
occurs when a
fragment of DNA
joins a
nonhomologous
chromosome.
Chromosome Abnormalities
Many chromosomal abnormalities can
occur on the sex chromosomes.
For example:
XXY- Kleinfelter’s Syndrome is
caused by an extra chromosome.
XO- Turner’s Syndrome is caused by
a missing chromosome.
Kleinfelter’s Syndrome
Karyotype of
a male with
an extra X
chromosome
Kleinfelter’s Syndrome
Male with
Kleinfelter’s
syndrome
Turner’s Syndrome
Karyotype of
a female
missing an X
chromosome
Turner’s Syndrome
The most common characteristics of Turner
syndrome include:
short stature
lack of ovarian development
webbed neck
arms that turn out slightly at the elbow
low hairline in the back of the head
also prone to cardiovascular problems, kidney
and thyroid problems, skeletal disorders such
scoliosis (curvature of the spine) or dislocated
hips, and hearing and ear disturbances.
Tracking Family Traits using Pedigrees
How might you learn if you have
genetic abnormalities or mutations in
your family?
In order to study heredity, scientists use
pedigrees to analyze a family history.
These help identify which relatives
exhibit certain traits.
Tracking Family Traits using Pedigrees
Pedigrees can
determine if a
trait is sex-linked
& whether a
particular trait is
dominant or
recessive.
Tracking Family Traits using Pedigrees
If a female carries the gene for a trait,
but does not actually have that trait she
is called a carrier.
In sex-linked traits mothers are usually
carriers that pass a trait on to their sons
on the X chromosome.
* Add to your notes!
Tracking Family Traits using Pedigrees
Look at the last page of your notes to
try and track the trait of albinism (a lack
of pigmentation) in a family by using a
pedigree.
Is the trait sex-linked?
Is the trait dominant or recessive?
Is it caused by one gene or by several?
ALBINISM