gene disorders - mostly very rare, recessive  

• mutations - source of all new alleles
• Tay-Sachs disease - causes lysosomes to burst
  • frequency of disease can vary w/ different populations and different histories
  • highest chance in Jewish populations
• natural selection can’t always get rid of all gene disorders
• Huntington disease - disorder caused by dominant gene
  • clinical symptoms don’t appear until middle age
  • those w/ disease have time to reproduce
  • natural selection doesn’t get rid of it
• Hemophilia - inability to form blood clots; cuts won’t stop bleading
• pedigree - graphical representation trait passed down many generations
  • uses history of the family to predict future phenotypes
• sickle-cell anemia - defect in hemoglobin carrier
  • alters shape of red blood cells
  • due to change in a single amino acid
  • those heterozygous for this disease have more resistance to malaria
• cystic fibrosis - mucus clogs lungs, liver, pancreas
  • due to failure of chloride ion transport protein

blood groups - 4 different phenotypes 

• codominant traits show effects of both alleles
• 3 alleles - IB (adds galactose), IA(adds galactosamine), i (doesn’t add sugar
• type A blood - IAIA homozygotes or IAi heterozygotes
• type B blood - IBIB homozygotes or IBi heterozygotes
• type AB blood - IAIB heterozygotes, universal acceptor
• type O blood - ii homozygotes, universal donor
• Rh blood group - cell surface markers on human red blood cells
  • Rh-negative people don’t have receptors
  • Rh-positive blood clump when immune system of Rh-negative people attack it

gene therapy - replacing defective genes w/ functional ones 

• cells w/ damaged genes fixed/replaced w/ working copies of the gene, then put into the body
• hard to reintroduce the fixed gene back into the body
  • using adenovirus (causes colds) activates the immune system, killing the vector
  • DNA inserted at a random location into the chromosome
• adeno-associated virus (AAV) - doesn’t cause a strong immune response, can still carry genes
  • less likely than adenovirus to produce cancer mutations