Inheritance

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