Transcript Genetic Disorders - Ms. George`s Science Class

Genetic
Disorders
Review
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Parents pass traits to their offspring
through their genes.
Genes are located on bigger
structures called chromosomes;
each person has 46 of these, which
are joined into 23 pairs.
Each parent contributes one-half of
each pair.
It's how those genes work together
that makes you unique!
Diseases
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Scientists have discovered that some
medical disorders are genetic.
Problems arise when the disease
gene is dominant or when the same
recessive disease gene is present on
both chromosomes in a pair.
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If a person carries the dominant gene
for a disease, he or she will usually have
the disease
Diseases caused by a dominant gene
include:
• Marfan syndrome (a connective tissue
disorder). People with Marfan have an
increased risk that their aorta will
enlarge and eventually rupture.
• Huntington disease
(a degenerative disease
of the nervous system).
Carriers
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People who have one recessive gene for a
disease are called carriers, and they don't
usually have the disease because they have
one normal, dominant gene. In other
words, their genotype for this trait is
heterozygous.
However, when two carriers have a child
together the child has a 1 in 4 (25%)
chance of getting the disease gene from
both parents, which results in the child
having the disease.
Examples of Recessive Disorders
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Disorders that occur when
recessive disease genes from
both parents come together
in a child. (homozygous
recessive)
• Cystic fibrosis (a lung
disease)
• Sickle cell anemia
(a blood disease)
• Tay-Sachs disease (which
causes nervous system
problems)
If both parents are
carriers (heterozygous)
what is the probability
that they will pass this
recessive gene to their
child?
Complete a Punnett
Square to model the
probabilities.
N =normal red blood
cell
n =sickle cell.
X-linked Genetic Disorders
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You have 23 pairs of genes and one of the
pairs determines what gender you are:
male or female
Boys: XY
Girls: XX
Some recessive genes are carried only on
the X chromosome, which means that
usually only males can develop the
disease because they have only one X
chromosome.
Females have two X chromosomes, so
they would need to inherit two copies of
the recessive gene to get the disease.
X-linked disorders
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X-linked disorders include color blindness
and the bleeding disorder hemophilia.
Hemophilia is a genetic disorder in which a
person's blood does not clot properly.
A person who has hemophilia has a
tendency to bleed excessively.
The Royal Courts of Europe provide an
interesting case study of hemophilia in a
family tree.
The “Royal Disease”
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Normally, hemophilia is quite rare.
But because royal families usually married
people from other royal families, there
was more of a chance that children would
inherit the gene for this trait.
Queen Victoria of England (1837-1901)
was a carrier of the hemophilia gene and
subsequently passed the disease on to
several royal families.
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Two of Queen Victoria's daughters,
Alice and Beatrice, were carriers of
hemophilia.
They passed the disease on to the
Spanish, German and Russian royal
families, ensuring that the disease
would be present in future
generations.
Genetic Mutation
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Some genetic disorders are caused
by mutations in genes.
Brainpop! Genetic Mutation