Section 18.4 Heredity

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Objectives

Explain how genetic information passes from one generation to the next.

Identify the causes of genetic disorders.

Section 18.4 Heredity

Compare the role of genes, environment, and behavior in affecting a person’s risk for disease.

Section 18.4 Heredity

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A widow’s peak and free earlobes are examples of dominant traits. What do you think a “dominant trait” is?

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?

Do you have free or attached earlobes?

Switch to QuickTake version of the quiz.

Widow’s Peak Smooth

Free Attached

Section 18.4 Heredity

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• 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.

The Basic Rules of Heredity

• Heredity is the passing on, or transmission, of biological traits from parent to child.

Section 18.4 Heredity

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• Chromosomes (KROH muh sohmz) are tiny structures found within cells that carry information about the characteristics you will inherit.

Chromosomes

• 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.

Section 18.4 Heredity

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• A gene is a section of a chromosome that determines or affects a characteristic, or trait.

Genes

• 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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• A dominant trait is one that appears in an offspring whenever its gene is present.

Dominant and Recessive Traits

• 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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• 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.

Heredity and Disease

• Genetic disorders are caused by the inheritance of an abnormal gene or chromosome.

Section 18.4 Heredity

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• Many genetic disorders, such as cystic fibrosis and hemophilia, are recessive traits.

Genetic Disorders

• 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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For: Updates on genetic disorders

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• Scientists know that a person’s risk for many diseases increases when close relatives have the disease.

Diseases With a Genetic Link

• 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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• For most diseases, your environment and your behavior affect your risk as much as or even more than your genes.

The Effect of Environment and Behavior

• 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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• Genetic Testing Genetic testing involves the analysis of a blood sample for the presence of abnormalities in specific genes.

Medical Advances

• 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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Vocabularyheredity 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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QuickTake Quiz

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Section 18.4 Heredity

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For: Chapter 18 self test

Section 18.4 Heredity

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End of Section 18.4

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