medelian

• Gregor Mendel


  (1822-1884) Responsible for the Laws governing Inheritance of Traits
• Gregor Johann Mendel


  • Austrian monk
  • Studied the inheritance of traits in pea plants
  • Developed the laws of inheritance
  • Mendel's work was not recognized until the turn of the 20th century
• Gregor Johann Mendel's experimental methods

  1. Cultivated and tested some 28,000 pea plants

  2. Found that the plants' offspring retained traits of the parents

  3. Hand-pollinated flowers using a paintbrush

  4. Snipped the stamens to prevent self-pollination

  5. Covered each flower with a cloth bag

  6. Traced traits through several generations

  
• Mendel stated that physical traits are inherited as "particles"
• Mendel did not know that the "particles" were actually Chromosomes & DNA

  
• Trait


  Any characteristic that can be passed from parent to offspring
• Heredity


  Passing of traits from parent to offspring
• Genetics


  Study of heredity
• Monohybrid cross


  Cross involving a single trait
• Dihybrid cross


  Cross involving two traits
• Punnett Square


  Used to help solve genetics problems

  
• Alleles


  Two forms of a gene (dominant & recessive)
• Dominant


  Stronger of two genes expressed in the hybrid; represented by a capital letter
• Recessive


  Gene that shows up less often in a cross; represented by a lowercase letter
• Genotype


  Gene combination for a trait (e.g. RR, Rr, rr)
• Phenotype


  The physical feature resulting from a genotype (e.g. red, white)
• Homozygous genotype


  Gene combination involving 2 dominant or 2 recessive genes (e.g. RR or rr); also called pure
• Heterozygous genotype


  Gene combination of one dominant & one recessive allele (e.g. Rr); also called hybrid
• Genes and Environment Determine Characteristics
• Why peas, Pisum sativum?

  • Can be grown in a small area
  • Produce lots of offspring
  • Produce pure plants when allowed to self-pollinate
  • Can be artificially cross-pollinated
• Reproduction in Flowering Plants

  1. Pollen contains sperm produced by the stamen

  2. Ovary contains eggs found inside the flower

  3. Pollen carries sperm to the eggs for fertilization

  4. Self-fertilization can occur in the same flower

  5. Cross-fertilization can occur between flowers
• Mendel's Experimental Methods


  1. Hand-pollinated flowers using a paintbrush

  2. Snipped the stamens to prevent self-pollination

  3. Covered each flower with a cloth bag

  4. Traced traits through several generations
• How Mendel Began

  Produced pure strains by allowing the plants to self-pollinate for several generations
• Eight Pea Plant Traits

  • Seed shape (Round (R) or Wrinkled (r))
  • Seed Color (Yellow (Y) or Green (yy))
  • Pod Shape (Smooth (S) or wrinkled (ss))
  • Pod Color (Green (G) or Yellow (g))
  • Seed Coat Color (Gray (G) or White (g))
  • Flower position (Axial (A) or Terminal (a))
  • Plant Height (Tall (T) or Short (t))
  • Flower color (Purple (P) or white (pp))

  
• The theoretical or expected ratio of plants producing round or wrinkled seeds is 3 round :1 wrinkled
• Mendel's observed ratio was 2.96:1
• The discrepancy is due to statistical error
• Parental P1 Generation


  The parental generation in a breeding experiment
• F1 generation


  The first-generation offspring in a breeding experiment (1st filial generation)
• F2 generation


  The second-generation offspring in a breeding experiment (2nd filial generation)
• Statistical error


  The larger the sample, the more nearly the results approximate to the theoretical ratio
• Generation "Gap"


  • P1 generation = the parental generation in a breeding experiment
  • F1 generation = the first-generation offspring in a breeding experiment (1st filial generation)
  • F2 generation = the second-generation offspring in a breeding experiment (2nd filial generation)
• Following the Generations


  1. Cross 2 pure plants (TT x tt)

  2. Results in all hybrids (Tt)
• Monohybrid Crosses


  • Trait: Seed Shape
  • Alleles: RR - Round, rr - Wrinkled

  
• P1 Monohybrid Cross


  1. RR x rr

  2. Offspring all Rr (hybrids)
• F1 Monohybrid Cross


  1. Rr x Rr

  2. Genotype: RR, Rr, rr

  3. Phenotype: Round & wrinkled

  4. Genotypic Ratio: 1:2:1

  5. Phenotypic Ratio: 3:1
• F2 Monohybrid Cross (1st)

  1. RR x Rr

  2. Genotype: RR, Rr

  3. Phenotype: Round

  4. Genotypic Ratio: 1:1

  5. Phenotypic Ratio: All alike
• F2 Monohybrid Cross (2nd)

  1. rr x Rr

  2. Genotype: Rr, rr

  3. Phenotype: Round & Wrinkled

  4. Genotypic Ratio: 1:1

  5. Phenotypic Ratio: 1:1
• Test Cross


  Homozygous dominant x Hybrid

  Homozygous recessive x Hybrid
• Inheritable factors or genes are responsible for all heritable characteristics