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Human Genetics

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
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