Chapter 12 Patterns of Heredity and Human Genetics Section 1 Mendelian Inheritance of Human Traits Pedigree • A pedigree is a • <> graphic representation of genetic inheritance. • Symbols are used to show the trait being studied and family relationships Answer the following about the above pedigree • a. What is the sex of I 1? ___________________ • b. How many children does IV 2 have? ___________ • c. How many children of IV 12 have cancer? ____________ • d. List all of the males who have polyps (carriers) __________ Dominant Autosomal Heredity • Follow Rule of Dominance • Tongue curling • Free earlobes • Huntington’s disease Huntington’s Disease • Lethal genetic disorder caused by rare autosomal dominant allele • Nervous system disintegrates causing loss of control of limbs and mental deterioration. Huntington’s disease • Since onset occurs between ages 30 and 50, this defect can be transmitted to new generations before the parent knows that he is a carrier. Huntington’s • Genetic testing can determine if a person is a carrier. • Carriers will get disease because allele is dominant. www.about-dementia.com/huntingtons/hd-causes.php Recessive Autosomal Heredity • Genetic disorders caused by recessive alleles. • Most genetic disorders are caused by this type of allele. • Cystic fibrosis, sickle -cell anemia, Tay - Sachs disease, Phenylketonuria (PKU). Cystic Fibrosis • Most common lethal genetic disorder in white Americans. • Characterized by thick mucus in lungs and digestive tract. • Food is not digested properly • Breathing is difficult - frequent lung infections Tay- Sachs • Absence of enzyme that breaks down a lipid that is produced and stored in the central nervous system. Lipid builds up in brain membranes • Common in Eastern European Jews and Pennsylvania Dutch. Symptoms of Tay-Sachs Disease • Blindness • Progressive loss of movement • Mental deterioration • Death by age 5. • See pg 312 for pedigree Phenylketonuria (PKU) • Most common in people of Norwegian and Swedish descent. • Caused by absence of enzyme that converts phenylalanine to tyrosine (amino acids). Symptoms of PKU • New born appears normal. • Once baby starts drinking milk, which is high in phenylalanine, damage occurs Symptoms • Build up in phenylalanine causes severe central nervous system damage resulting in mental retardation. Treatment of PKU • All newborns are tested for PKU. • Changes in diet can prevent damage. New Problems With PKU • If a homozygous recessive female becomes pregnant, high levels of phenylalanine in her blood can damage baby.
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