Download Genetic Disorders and Hereditary Diseases

NOTES 24 – Genetic Disorders
and Hereditary Diseases
What is a genetic disorder?
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A genetic disorder is a condition caused
by any abnormality in a person’s genes or
chromosomes
Genetic disorders have 2 main causes
Cause #1
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An error during meiosis causes a sperm
cell or an egg cell to have some defect.
If one of these gametes is involved in
fertilization, it usually results in
miscarriage, but in a few cases, a baby
will develop and be carried to term with a
genetic disorder
EX. Down Syndrome is caused by an extra
21st chromosome in the sperm or egg cell
Cause #2
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A defective gene present in one or both of
the parents is inherited directly by the
child causing a disorder
These kinds of disorders are calle
hereditary diseases and follow the
same rules of inheritance as other human
traits
Hereditary Diseases Caused by
Dominant Genes
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Only one copy of the gene (from either
parent) is needed for a person to have the
disease
A person with a dominant hereditary
disease usually has at least one affected
parent
Parents have a 50% chance of passing
these types of diseases to children
Ex. Huntington’s Disease
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Caused by the inheritance of a dominant gene
Affects the nervous system
Produces incorrect protein that eventually leads
to destruction of brain cells
Symptom’s include abnormal body movements,
lack of coordination, impaired mental abilities
and altered personality
Patients generally live 15 to 20 years after the
appearance of the first symptoms
Currently no cure
Hereditary Diseases Caused by
Recessive Genes
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Two copies of the defective gene must be
inherited (one from each parent)
Affected persons usually have two nonaffected parents who are carriers
Two carrier parents have a 25% chance of
having a child with the disease
Ex. Sickle-Cell Anemia
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Caused by the inheritance of two recessive
genes
Causes red blood cells to be abnormally shaped
Cells may stick to each other or become stuck in
blood vessels preventing oxygen flow which may
lead to organ damage or stroke
Individuals are often well, but experience
painful, possibly fatal attacks from time to time
Sickle Cell Anemia
Hereditary Disease Caused by SexLinked Recessive Genes
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Caused by defective genes carried on the
X chromosome
Males affected more than women
Males inherit one defective gene on X
from mother to have disorder
Females only affected if they inherit 2
defective genes (one from each parent)
Ex. Hemophilia
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Caused by the inheritance of
one recessive gene on the X
(males) or two recessive
genes on both X’s (females)
Affects blood – blood does
not clot
Leads to severely increased
risk of bleeding from common
injuries
Potentially fatal
Hemophilia