Agustina Mandolini

• Genotype


  The allele combination for a specific trait
• Types of allele combinations

  • Homozygous - Both alleles are the same (e.g. AA)
  • Heterozygous - Alleles are different (e.g. Aa)
  • Hemizygous - Only one allele (e.g. X/Y genes in males)
• Phenotype


  The physical expression of a specific trait
• Phenotype is determined by genotype and environmental factors
• Gregor Mendel


  Established the principles of inheritance via experimentation (he crossed large numbers of pea plants)
• Mendel's findings


  • Organisms have heritable factors (genes)
  • Parents contribute equally to inheritance by supplying one version of the gene each (alleles)
  • Gametes contain only one allele of each gene (haploid)
  • Fusion of gametes results in zygotes with two alleles of each gene (diploid)
• The separation of the two alleles of each gene into separate haploid gametes occurs via meiosis
• Complete Dominance


  One allele is expressed over another
• Complete Dominance


  • Dominant allele is expressed in heterozygote (capital letter)
  • Recessive allele is masked in heterozygote (lower case letter)
• A recessive phenotype can only be expressed in homozygotes
• Codominance


  Both alleles are equally expressed in the phenotype
• ABO blood system


  • A
  • B
  • AB
  • O
• Genetic diseases can be due to recessive, dominant or codominant alleles
• Recessive conditions are most common, as heterozygotes are carriers
• Autosomal Recessive


  Cystic fibrosis is caused by a mutated CFTR gene (chromosome 7) and produces thick mucus that clogs airways and causes respiratory issues
• Autosomal Dominant


  Huntington's disease is caused by a mutated HTT gene (chromosome 4) and an amplification of CAG repeats (>40) leads to neurodegeneration
• Autosomal Codominant


  Sickle cell anemia is caused by a mutated HBB gene (chromosome 11) and sickling of blood cells leads to anemia and other complications
• Radiation and mutagenic chemicals increase mutation rates and can cause genetic diseases
• Most genetic diseases in humans are rare
• Radiation exposure

  • Nuclear bombing of Hiroshima (1945)
  • Accident / meltdown in Chernobyl (1986)
• Long-term consequences of radiation exposure

  • Increased incidence of cancer
  • Reduced immunity (⬇︎ T cell count)
  • Congenital abnormalities (Chernobyl only)
  • Variety of organ-specific health effects (e.g. liver cirrhosis, cataract induction, etc)