ads Figure 16.4 Two common patterns of autosomal inheritance in humans. & Both parents are heterozygous. b. One parent is heterozygous, and the other is homozygous recessive. The letter A stands for any trait that is dominant, and the letter a stands for any trait that is recessive Substitute the correct alleles for the problems you are working on. For example, C normal c= cystic fibrosis o Parents d Parents 9 A A A4 a Au eggs Offspring 2 Key A Dominant ale Dominant phenotype Recessive phenotype Phenotypic Ratio sperm % X 40 eggs Offspring an An Ga Kay A Dominant alle -Recessive sele Dominant phenotype Recessive phenotype Phenotypic Ratio Autosomal Disorders 1. Neurofibromatosis (NF), sometimes called von Recklinghausen disease, is one of the most common genetic disorders. It affects roughly 1 in 3,000 people. At birth or later. the affected individual may have six or more large, tan spots on the skin. Such spots may increase in size and number and become darker. Small, benign tumors (lumps) called neurofibromas may occur under the skin or in the muscles. Neurofibromatosis is an autosomal dominant disorder. If a heterozygous woman reproduces with a homozygous normal man, what are the chances a child will have neurofibromatosis? 2. Cystic fibrosis is due to abnormal mucus-secreting tissues. At first, the infant may have difficulty regaining the birth weight despite good appetite and vigor. Symptoms include a cough with rapid respiratory rate and large, frequent, and foul-smelling stools due to abnormal pancreatic secretions. Whereas children previously died in infancy due to infections, they now often survive because of antibiotic therapy. Cystic fibrosis is an autosomal recessive disorder. A carrier is an individual that appears to be normal but carries a recessive allele for a genetic disorder. A man and a woman are both carriers ( -) for cystic fibrosis. What are the chances a child will have cystic fibrosis? 3. Huntington disease does not appear until the 30s or early 40s. There is a progressive deterioration of the individual's nervous system, which eventually leads to constant thrashing and writhing movements until insanity precedes death. Studies suggest that Huntington disease is pleiotropic. This is when a single gene has multiple effects. Huntington disease is an autosomal dominant disorder. Drina is 25 years old and as yet has no signs of Huntington disease. Her mother does have Huntington disease -), but her father is free ( ( ) of the disorder. What are the chances that Drina will develop Huntington disease?