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Chapter 11: Complex Inheritance and Human Heredity

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Chapter 11: Complex Inheritance and Human Heredity Complex Inheritance and Human Heredity Two X chromosomes of a human female Colored LM Magnification: 9500؋ Section 1 Basic Patterns of Human Inheritance -!). )DEA The inheritance of a trait over several generations can be shown in a pedigree. Section 2 Complex Patterns of Inheritance -!). )DEA Complex inheritance of traits does not follow inheritance patterns described by Mendel. Section 3 Chromosomes and Human Heredity -!). )DEA Chromosomes can be studied using karyotypes. BioFacts • Sometimes different ethnic groups can be distinguished by phenotypic traits such as skin color, hair color, and skin folds at the corner of the eyes. • The individual genetic ▶ differences within an ethnic ▶ group can be greater than the genetic differences between individuals of two different ethnic groups. X and Y chromosomes of a human male ▶ Colored LM Magnification: 9500؋ ▶ 294 ((t)Addenbrookest)Addenbrookes HHospital/Photoospital/Photo RResearchers,esearchers, ((b)Addenbrookesb)Addenbrookes HHospital/Photoospital/Photo ResearchersResearchers , ((bkgd)Annebkgd)Anne AAckerman/Gettyckerman/Getty ImagesImages 2294-295_C11_CO_869510.indd94-295_C11_CO_869510.indd 229494 44/28/06/28/06 11:40:19:40:19 PPMM SStart-Uptart-Up AActivitiesctivities Genetic Disorders Make LAUNNCHCH LLabab this Foldable to help you understand how variations in What do you know nucleotide base sequences are about human inheritance? linked to genetic disorders. As knowledge and understanding of human inheri- STEP 1 Fold a sheet of notebook paper tance increases, long-standing ideas regarding the lengthwise, leaving a half inch between facts of human heredity must be reexamined. Any the folds as shown. ideas disproven by new discoveries must be rejected. Procedure 1. Read the statements below carefully and determine whether they are true or false. Statements: A. The father determines the gender of the child. B. Individuals may transmit characteristics to their offspring which they themselves do STEP 2 Rotate the paper and cut the not show. top layer to form eight tabs of equal size, C. Identical twins always are of the same as shown. gender. 2. Discuss your answers with your classmates and teacher. Analysis 1. Assess What question was missed most often by the entire class? Discuss reasons why. 2. Analyze Why is it helpful to understand STEP 3 Label each tab with the name human heredity? of a different genetic disorder. Under the tabs, write about each disorder. Visit biologygmh.com to: /,$!",%3 ▶ study the entire chapter online & Use this Foldable with Section 11.1. As you study the section, note ▶ explore the Concepts in Motion, the Interactive Tables, Microscopy Links, how to trace genetic disorders using pedigrees. Virtual Labs, and links to virtual dissections ▶ access Web links for more information, projects, and activities ▶ review content online with the Inter- active Tutor and take Self-Check Quizzes Chapter 11 • ComplexSection Inheritance 1 • XXXXXXXXXXXXXXXXXX and Human Heredity 295 2294-295_C11_CO_869510.indd94-295_C11_CO_869510.indd 229595 44/28/06/28/06 11:40:46:40:46 PPMM Section 11..11 Objectives Basic Patterns ◗ Analyze genetic patterns to determine dominant or recessive of Human Inheritance inheritance patterns. ◗ Summarize examples of dominant and recessive disorders. -!). )DEA The inheritance of a trait over several generations can ◗ Construct human pedigrees from be shown in a pedigree. genetic information. Real-World Reading Link Knowing a purebred dog’s ancestry can help the Review Vocabulary owner know health problems that are common to that dog. Similarly, tracing genes: segments of DNA that control human inheritance can show how a trait was passed down from one generation the production of proteins to the next. New Vocabulary carrier Recessive Genetic Disorders pedigree #ONNECTION TO (ISTORY Mendel’s work was ignored for more than 30 years. During the early 1900s, scientists began to take an interest in hered- ity, and Mendel’s work was rediscovered. About this time, Dr. Archibald Garrod, an English physician, became interested in a disorder linked to an enzyme deficiency called alkaptonuria (al kap tuh NYUR ee uh), which results in black urine. It is caused by acid excretion into the urine. Dr. Garrod observed that the condition appeared at birth and continued throughout the patient’s life, ultimately affecting bones and joints. He also noted that alkaptonuria ran in families. With the help of another scientist, he determined that alkaptonuria was a recessive genetic disorder. Today, progress continues to help us understand genetic disorders. Review Table 11.1, and recall that a recessive trait is expressed when the individual is homozygous recessive for that trait. Therefore, those with at least one dominant allele will not express the recessive trait. An individual who is heterozygous for a recessive disorder is called a carrier. Review Table 11.2 as you read about several recessive genetic disorders. Interactive Table To explore more Table 11.1 Review of Terms about human inheritance, visit biologygmh.com. Term Example Definition True-breeding yellow-seed An organism with two of the same alleles for pea plants would be YY, a particular trait is said to be homozygous for Homozygous and green-seed pea plants that trait. would be yy. A plant that is Yy would An organism with two different alleles for a be yellow-seed pea. particular trait is said to be heterozygous for that Heterozygous trait. When alleles are present in the heterozy- gous state, the dominant trait will be observed. 296 Chapter 11 • Complex Inheritance and Human Heredity 2296-301_C11_S1_869510.indd96-301_C11_S1_869510.indd 229696 44/25/06/25/06 88:36:18:36:18 AAMM Interactive Table To explore more Table 11.2 Recessive Genetic Disorders in Humans about recessive genetic disorders, visit biologygmh.com. Occurrence Disorder Cause Effect Cure/Treatment in the U.S. 1 in 3500 The gene that codes for • Excessive mucus • No cure a membrane protein is production • Daily cleaning of mucus from Cystic fibrosis defective. • Digestive and the lungs respiratory failure • Mucus-thinning drugs • Pancreatic enzyme supplements 1 in 17,000 Genes do not produce • No color in the skin, • No cure normal amounts of the eyes and hair • Protect skin from the Sun and Albinism pigment melanin. • Skin susceptible to other environmental factors UV damage • Visual rehabilitation • Vision problems 1 in 50,000 to Absence of the gene that • Mental disabilities • No cure Galactosemia 70,000 codes for the enzyme that • Enlarged liver • Restriction of lactose/ breaks down galactose • Kidney failure galactose in the diet 1 in 2500 Absence of a necessary • Buildup of fatty • No cure or treatment Tay-Sachs (affects people of enzyme that breaks down deposits in the brain • Death by age 5 disease Jewish descent) fatty substances • Mental disabilities Cystic fibrosis One of the most common recessive genetic disorders among Caucasians is cystic fibrosis, which affects the mucus-producing glands, digestive enzymes, and sweat glands. Chloride ions are not absorbed into the cells of a person with cystic fibrosis but are excreted in the sweat. Without sufficient chloride ions in cells, water does not diffuse &/,$!",%3 from cells. This causes a secretion of thick mucus that affects many areas Incorporate information of the body. The thick mucus clogs the ducts in the pancreas, interrupts from this section into digestion, and blocks the tiny respiratory pathways in the lungs. Patients your Foldable. with cystic fibrosis are at a higher risk of infection because of excess mucus in their lungs. Treatment for cystic fibrosis currently includes physical therapy, medication, special diets, and the use of replacement digestive enzymes. Genetic tests are available to determine whether a person is a carrier, indicating they are carrying the recessive gene. Albinism In humans, albinism is caused by altered genes, resulting in the absence of the skin pigment melanin in hair and eyes. You will learn more about melanin in Chapter 32. Albinism is found in other animals as well. A person with albinism has white hair, very pale skin, and pink pupils. The absence of pigment in eyes can cause problems with vision. Although we all must protect our skin from the Sun’s ultraviolet radiation, those with albinism need to be especially careful. Tay-Sachs disease Tay-Sachs (TAY saks) disease is a recessive genetic disorder. Its gene is found on chromosome 15. Often identified by a cherry-red spot on the back of the eye, Tay-Sachs disease (TSD) seems to be predominant among Jews of eastern European descent. Section 1 • Basic Patterns of Human Inheritance 297 2296-301_C11_S1_869510.indd96-301_C11_S1_869510.indd 229797 44/25/06/25/06 88:36:24:36:24 AAMM VOCABULARY TSD is caused by the absence of the enzymes responsible for break- ACADEMIC VOCABULARY ing down fatty acids called gangliosides. Normally, gangliosides are Decline: made and then dissolved as the brain develops. However, in a person to gradually waste away; or a down- affected by Tay-Sachs disease, the gangliosides accumulate in the brain, ward slope inflating brain nerve cells and causing mental deterioration. His health declined because of the disease. Galactosemia Galactosemia (guh lak tuh SEE mee uh) is a recessive genetic disorder characterized by the inability of the body to digest galactose. During digestion, lactose from milk breaks down into galac- tose and glucose. Glucose is the sugar used by the body for energy and circulates in the blood. Galactose must be broken down into glucose by an enzyme named GALT. Persons who lack or have defective GALT cannot digest galactose. Persons with galactosemia should avoid milk products. Dominant Genetic Disorders Not all genetic disorders are caused by recessive inheritance. As described in Table 11.3, some disorders, such as the rare disorder Huntington’s disease, are caused by dominant alleles. That means those who do not have the disorder are homozygous recessive for the trait. Huntington’s disease The dominant genetic disorder Huntington’s disease affects the nervous system and occurs in one out of 10,000 people in the U.S.
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