Lesson 1

• Genetics


  The study of heredity
• Traits


  • Controlled by genes
  • Form two alleles
  • Which may be dominant or recessive
• Gregor Mendel


  • Proposed
  • Principle of paired unit factors
  • Law of Dominance and Recessiveness
  • Law of Independent Assortment
  • Law of Segregation
• The principles of genetics can be traced back to centuries ago in the breeding of plants and animals
• Farmers learned the importance of choosing ideal parent plants and animals to improve crops and livestock
• Blood Theory of Heredity


  Gave rise to expressions like bloodlines, blue blood, blood relative
• Gregor Mendel


  • Austrian Monk
  • Physics and Natural History teacher
  • Conducted biological experiments in a small garden
  • 1856-1863
  • Pisum sativum (garden pea)
  • Discovered basic principles of inheritance
• Reasons for Mendel choosing garden peas: Several varieties, self-pollination
• Mendel's Experiment


  1. Pea plants normally self-pollinate

  2. Removed stamens from purple flower

  3. Transferred pollen from stamens of white flower to carpel of purple flower

  4. Pollinated carpel matured into pod

  5. Planted seeds from pod
• Traits observed in Mendel's garden pea experiments

  • Flower color
  • Flower position
  • Plant height
  • Seed texture
  • Seed color
  • Pea pod texture
  • Pea pod color
• Hybrid


  Offspring of parents with different traits
• P Generation


  Parental (starting breeding plants)
• F1 Generation


  First filial generation
• F2 Generation


  Second filial generation, resulted in hybrids with dominant and recessive traits reappearing in a 3:1 ratio
• Dominant traits


  Traits that appeared in the first generation
• Recessive traits


  Traits that were masked
• Alleles


  Different forms of a gene
• Phenotype


  Observable characteristics
• Genotype


  Genetic makeup
• Homozygous


  Identical pair of alleles for a trait
• Heterozygous


  Mixed pair of alleles for a trait
• Principle of Paired Unit Factors


  Characters are controlled by hereditary particles called unit factors (come in pairs)
• Law of Dominance and Recessiveness


  If an organism inherits different alleles for the same trait, one allele may be dominant over the other
• Law of Segregation


  1. Each gene and organism receives one allele from each parent

  2. Segregation - maternal and paternal alleles separate into different gametes

  3. Fertilization - male and female gametes randomly combine
• Law of Independent Assortment

  Segregation of one pair of alleles is independent of the segregation of other pairs during gamete formation
• Mendel's work was rediscovered in 1900, triggering the search for evidence of his factors of inheritance
• Walter S. Sutton published the Chromosome Theory of Inheritance in 1903, showing that genes are located in chromosomes and their behavior during meiosis and fertilization accounts for inheritance patterns
• Similarities between Mendel's factors and Sutton's chromosome theory


  • Hereditary factors/Chromosomes occur in pairs
  • Factors/Chromosomes segregate during gamete formation
  • Factors/Chromosome pairs assort independently