Heredity and Genetics (2:39) Click here to launch video Click here to download print activity

Certain traits, such as eye and hair color, come from both parents.

chromosomes genes DNA genetic disorders amniocentesis chorionic villi sampling gene therapy

Heredity Heredity is the passing of physical traits from parents to their children. All the characteristics you have, such as your eye color, the amount of curl in your hair, and your height, are determined by your genetic code.

Heredity Family members often share similar physical traits.

Heredity Most of the cells in the human body contain 46 chromosomes that are arranged in 23 pairs. Chromosomes Thread-like structures found within the nucleus of a cell that carry the codes for inherited traits

Heredity Genes are sections of chromosomes that occur in pairs. One gene from each pair is inherited from each parent. Genes The basic units of heredity

DNA All living things are made of DNA, or deoxyribonucleic acid. DNA The chemical unit that makes up chromosomes

DNA DNA like this double helix, looks like a long twisted ladder.

Genetics and Fetal Development Chromosomes from a sperm and an egg unite to carry the hereditary traits from parents. Passing on traits from parent to child involves genetics.

Genetics and Fetal Development Most human cells have 46 chromosomes, or 23 pairs. However, egg and sperm cells have half that number—23 chromosomes.

Genetics and Fetal Development When a sperm and egg unite during fertilization, the resulting zygote will have 46 chromosomes: 23 from the mother’s egg and 23 from the father’s sperm.

Dominant and Recessive Genes Some genes are dominant, while others are recessive. The traits of recessive genes usually appear only when the dominant genes are not present.

Dominant and Recessive Genes Because females have only X chromosomes, their egg cells contain only an X chromosome. Sperm contain either an X or a Y chromosome. Thus, the sperm from the male determines the gender of a child.

Genetic Disorders Genetic disorders are caused by defects in genes. Most genetic disorders cannot be cured, but some can be treated.

Genetic Disorders A person can inherit genes that contain a mutation, or abnormality. The mutation may have little or no effect. It also may result in a birth defect or may increase the person’s likelihood of developing a disease.

Genetic Disorders Some genetic disorders are apparent at birth. Genetic disorders Disorders caused partly or completely by a defect in genes

Genetic Disorders Amniocentesis is used to test for genetic disorders. Amniocentesis A procedure in which a syringe is inserted through a pregnant female’s abdominal wall to remove a sample of the amniotic fluid surrounding the developing fetus

Genetic Disorders Common Human Genetic Disorders Failure of blood to clot Hemophilia Varying degrees of mental retardation, short stature, round face with eyelids that cover inner corners of the eyes Down Syndrome Mucus clogs many organs, including lungs, liver, and pancreas; nutritional problems; serious respiratory infections and congestion Cystic Fibrosis Destruction of nervous system; blindness; paralysis; death during early childhood Tay-Sachs Disease Red blood cells have a sickle shape and clump together; may result in severe joint and abdominal pain, weakness, kidney disease, restricted blood flow Sickle Cell Anemia

Genetic Disorders Chorionic villi sampling is used to test for genetic disorders. Chorionic villi sampling A procedure in which a small piece of membrane is removed from the chorion, a layer of tissue that develops into the placenta

Battling Genetic Diseases Research is ongoing to correct genetic disorders. Research into the human genome has given scientists a greater understanding of how genetic diseases progress.

Battling Genetic Diseases Gene therapy is an experimental treatment for correcting genetic disorders. Gene therapy The process of inserting normal genes into human cells to correct genetic disorders

Genetic Counseling Genetic counselors can guide families of children with genetic disorders on treatment options.

Genetic Counseling Though genetic engineering, some vaccines that can prevent disease have been produced.

After You Read Reviewing Facts and Vocabulary Chromosomes are found within the nucleus of a cell and carry the codes for inherited traits. The chromosomes contain genes, which are the basic units of heredity. 1.Define the terms chromosomes and genes.

After You Read Reviewing Facts and Vocabulary 2.How many chromosomes are found in most human cells? How many are found in egg and sperm cells? Most human body cells have 46 chromosomes, but egg and sperm cells have 23 chromosomes.

After You Read Reviewing Facts and Vocabulary 3.Identify the difference between the chromosomes of a male and the chromosomes of a female. Males have an X and a Y chromosome. Females have two X chromosomes.