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Inheritance Pleiotropy Single gene may affect multiple traits

Inheritance Pleiotropy Single gene may affect multiple traits Single gene products may affect many cells or cell types in different ways Ex: Cystic fibrosis, sickle cell disease Epistasis Presence of certain alleles at one locus can alter expression of alleles at different locus

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Inheritance Pleiotropy Single gene may affect multiple traits

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  1. Inheritance • Pleiotropy • Single gene may affect multiple traits • Single gene products may affect many cells or cell types in different ways • Ex: Cystic fibrosis, sickle cell disease • Epistasis • Presence of certain alleles at one locus can alter expression of alleles at different locus • Ex: Coat color in dogs • Color regulated by one allele pair (B = Black, b = brown) • Second allele pair (E = active, e = inactive) regulates deposition of color in hair • EE and Ee dogs are pigmented, ee dogs are yellow • Gene for pigment deposition is epistatic to gene that codes for Black or brown pigment

  2. Fig. 14.12

  3. Inheritance • Polygenic Inheritance • Some traits controlled by alleles at multiple loci • Alleles may have additive effects • Ex: Skin color and height in humans • Skin color governed by alleles at three unlinked loci (simplified) • Alleles incompletely dominant with additive effects • AABBCC = Darkest skin color • aabbcc = Lightest skin color • Population typically shows normal distribution of trait

  4. Fig. 14.13

  5. Human Genetics • Requires different methods than those for animals and plants • Controlled mating experiments with true-breeding strains not possible • Pedigree Analysis • Study of readily identifiable traits

  6. Fig. 14.15

  7. Human Genetic Disorders • Most from mutations of single genes • Most autosomal recessive • Some autosomal dominant • Autosomal Recessive • Expressed only in homozygous recessive individuals • Heterozygous individuals = carriers

  8. Human Genetic Disorders • Autosomal Recessive • Phenylketonuria (PKU) • Inability to synthesize enzyme that converts phenylalanine to tyrosine • Phenylalanine  toxic compound  nervous system damage  severe mental retardation • Damage usually occurs just after birth • Preventable; screening + low phenylalanine diet • Most common in people of W. European descent • Cystic fibrosis (CF) • Abnormal Cl- transport protein  accumulation of abnormally thick mucus in lungs, pancreas, reproductive system • Mucus hosts bacteria  infections, tissue damage • Most common genetic disorder in people of W. European descent • 5% of US residents are carriers

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