Download Section 18.4

Section 18.4 Heredity
Heredity
Objectives
Explain how genetic information passes from
one generation to the next.
Identify the causes of genetic disorders.
Compare the role of genes, environment, and
behavior in affecting a person’s risk for
disease.
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Section 18.4 Heredity
Quick Quiz Take a brief self-inventory of some of your physical
traits, or characteristics.
Do you have a
widow’s peak or a
smooth hairline?
Widow’s Peak
Smooth
Do you have free or
attached earlobes?
Free
Attached
A widow’s peak and free earlobes are examples of dominant
traits. What do you think a “dominant trait” is?
Switch to QuickTake version of the quiz.
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Section 18.4 Heredity
The Basic Rules of Heredity
• Children's eye color, the shape of their ears, and
their height are all determined in part from the
genetic information they inherit from their parents.
• Heredity is the passing on, or transmission, of
biological traits from parent to child.
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Section 18.4 Heredity
Chromosomes
• Chromosomes (KROH muh sohmz) are tiny structures
found within cells that carry information about the
characteristics you will inherit.
• Most of the cells in your body contain 23 pairs of
chromosomes.
• When a sperm and egg unite, the fertilized egg ends
up with 46 chromosomes—23 from each parent.
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Section 18.4 Heredity
Genes
• A gene is a section of a chromosome that
determines or affects a characteristic, or trait.
• Genes come in pairs.
• Hereditary information passes from one generation
to the next through genes contained on the two sets
of chromosomes that a person receives from their
parents.
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Section 18.4 Heredity
Dominant and Recessive Traits
• A dominant trait is one that appears in an offspring
whenever its gene is present.
• A recessive trait appears in an offspring only when
the dominant form of the gene is not present.
• The rules of heredity for most traits are complex.
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Section 18.4 Heredity
Heredity and Disease
• Just like earlobe shape, eye color, and other inherited
traits, an abnormal condition known as a genetic
disorder can be passed from parent to child.
• Genetic disorders are caused by the inheritance of an
abnormal gene or chromosome.
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Section 18.4 Heredity
Genetic Disorders
• Many genetic disorders, such as cystic fibrosis and
hemophilia, are recessive traits.
• A few disorders, such as Huntington’s disease, are
dominant traits.
• Other genetic disorders, such as Down syndrome,
are the result of too few or too many chromosomes.
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Section 18.4 Heredity
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Section 18.4 Heredity
For: Updates on genetic disorders
Click above to go online.
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Section 18.4 Heredity
Diseases With a Genetic Link
• Scientists know that a person’s risk for many diseases
increases when close relatives have the disease.
• Some diseases for which a genetic link is suspected or
has been identified are
• breast cancer
• colon cancer
• high blood pressure
• diabetes
• some forms of Alzheimer’s disease
• Many different genes affect the development of disease.
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Section 18.4 Heredity
The Effect of Environment and Behavior
• For most diseases, your environment and your
behavior affect your risk as much as or even more
than your genes.
• Exposure to environmental risk factors is sometimes
not in your control.
• Among the factors you can control are your habits
or behaviors.
• Making wise choices now will greatly decrease your
risk for disease later on in life.
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Section 18.4 Heredity
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Section 18.4 Heredity
Medical Advances
• Genetic Testing Genetic testing involves the
analysis of a blood sample for the presence of
abnormalities in specific genes.
• Gene Therapy Scientists are currently researching
a technique in which healthy copies of a gene are
delivered to the cells of a person who has a defective
copy of the gene.
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Section 18.4 Heredity
Vocabulary
heredity
All the traits that are passed from parent to child;
the biological process of passing on, or
transmitting, those traits.
chromosome
The tiny structures found within cells that carry
information about inherited characteristics.
gene
A section of a chromosome that determines or
affects a characteristic, or trait.
genetic disorder
A disorder caused by the inheritance of an
abnormal gene or chromosome.
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Section 18.4 Heredity
QuickTake Quiz
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Section 18.4 Heredity
For: Chapter 18 self test
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Section 18.4 Heredity
End of Section 18.4
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