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Human Biology Sylvia S. Mader Michael Windelspecht Chapter 20 Patterns of Genetic Inheritance Lecture Outline Part 3 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 1 20.3 Inheritance of Genetic Disorders Autosomal recessive disorders of interest • ________________ – lack of the enzyme that breaks down fatty acid proteins in lysosomes results in accumulation • ________________ – Cl- ions do not pass normally through a cell membrane, resulting in thick mucus in lungs and other places, often causing infections 2 20.3 Inheritance of Genetic Disorders Autosomal recessive disorders of interest • Phenylketonuria (PKU) – lack of an enzyme needed to make a certain amino acid; affects nervous system development • Sickle-cell disease – red blood cells are sickleshaped rather than __________, resulting in clogged blood vessels 3 20.3 Inheritance of Genetic Disorders Tay-Sachs disease Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. lysosomes Healthy neuron bulging lysosomes Neuron affected by Tay–Sachs Figure 20.10 Neuron affected by Tay–Sachs disease. 4 20.3 Inheritance of Genetic Disorders Autosomal dominant disorders of interest • __________ syndrome – defect in the production of the elastic connective tissue protein fibrillin; results in dislocated lens, long limbs and fingers, caved-in chest, and weak wall of aorta • Osteogenesis imperfecta – defect in collagen synthesis; results in weakened, brittle bones • ______________ – huntington protein has too many glutamine amino acids, leading to the progressive degeneration of brain cells 5 20.3 Inheritance of Genetic Disorders Marfan syndrome Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Connective tissue defects Skeleton Chest wall deformities Long, thin fingers, arms, legs Scoliosis (curvature of the spine) Flat feet Long, narrow face Loose joints Heart and blood vessels Mitral valve prolapse Enlargement of aorta Eyes Lungs Skin Lens dislocation Severe nearsightedness Collapsed lungs Stretch marks in skin Recurrent hernias Dural ectasia: stretching of the membrane that holds spinal fluid Aneurysm Aortic wall tear (top right): © Ed Reschke Figure 20.16 Marfan syndrome. 6 20.3 Inheritance of Genetic Disorders Genetic disorders Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. H2O Cl– Cl– Cl H2O Cl– H2O Cl nebulizer many neurons in normal brain defective channel percussion vest thick mucus loss of neurons in Huntington brain © Pat Pendarvis (both): Courtesy Dr. Hemachandra Reddy, The Neurological Science Institute, Oregon Health & Science University Figure 20.12 Huntington disease. Figure 20.11 Cystic fibrosis disease. 7 20.4 Beyond Simple Inheritance Patterns Polygenic inheritance • Polygenic traits – 2 or more sets of alleles govern 1 trait – Each dominant allele codes for a product, so these effects are additive. – This results in a continuous variation of phenotypes. – Environmental effects cause intervening phenotypes. – e.g., skin color ranges from very dark to very light – e.g., height varies among individual humans 8 20.4 Beyond Simple Inheritance Patterns Polygenic inheritance • Multifactorial trait – a polygenic trait that is particularly influenced by the environment – e.g., skin color is influenced by sun exposure – e.g., height can be affected by nutrition 9 20.4 Beyond Simple Inheritance Patterns Polygenic inheritance Frequency Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. aabbcc Aabbcc aaBbcc aabbCc 0 1 AaBbcc AabbCc aaBbCc AAbbcc aaBBcc aabbCC AaBbCc aaBbCC AAbbCc AabbCC AABbcc aaBBCc AaBBcc aaBBCC AAbbCC AABBcc AaBbCC AaBBCc AABbCc 2 3 4 Number of dominant alleles AaBBCC AABbCC AABBCc AABBCC 5 6 Figure 20.14 Polygenic inheritance and skin color. Number most are this height few 62 short 64 few 66 68 70 72 74 tall Height in Inches Figure 20.13 Height is a polygenic trait in humans. Courtesy University of Connecticut/Peter Morenus, photographer 10 20.4 Beyond Simple Inheritance Patterns Demonstrating environmental influences on phenotype • Himalayan rabbit’s coat color is influenced by temperature. • There is an allele responsible for melanin production that appears to be active only at lower temperatures. • The extremities have a lower temperature and thus the ears, nose, paws, and tail are dark in color. Figure 20.15 Himalayan rabbit with temperature-susceptible coat color. 11