• P generation: Parental generation, Mendel crossed a purebred purple with a purebred white plant
    • People used to believe in blending inheritance: traits are mixed
      • Ex: a tall person mates with short person = medium height baby
    • F1 generation: created only purple plants, traits didn’t blend → proved blending inheritance wrong
    • F2 generation: offspring produced by breeding F1 Generation; Mendel bred purple hybrids and created 75% purple and 25% white flowers
      • Showed that traits do not blend together, can be hidden and come out in a later generation

Types of Crosses

  1. Monohybrid cross: only one trait (ex: stem length)                                                                                                                                       
  2. Dihybrid Cross: investigating two traits (Ex: stem length and flower color)  [16 squares → use FOIL]
  • For dihybrids, the ratio is D/D : D/r : r/D : r/r
  • Testcross: find out the unknown allele that corresponds with the dominant phenotype of an organism
    • Cross the dominant organism with a homozygous recessive organism, if any of their offspring are recessive, then the dominant organism is heterozygous (Bb)

Important Ratios

  • 3:1 → Heterozygous x Heterozygous monohybrid cross
    • 1:2:1 genotypic ratio
  • 9:3:3:1 → dihybrid cross in which all alleles undergo independent assortment (unlinked)
    • Heterozygous x Heterozygous
  • 4:4:4:4 → Heterozygous x Homozygous dihybrid cross

Mendel’s Law of Inheritance

Law of Segregation

  • Describes how alleles are segregated into different gametes and reunited after fertilization
  • During anaphase I, homologs separate randomly to opposite poles so that each gamete only receives one copy of each allele
    • Describes alleles of same gene
  • Process in meiosis that ensures gametes get both maternal and paternal chromosomes

Mendel’s Law of Independent Assortment

  • Every character is inherited on its own bcuz alleles of different genes randomly orient during metaphase I and are sorted independent of the other one.
    • In other words, the allele a gamete receives for one gene does not influence the allele received for another gene
      • Brown hair doesn’t mean you will get brown eyes
    • The behavior of one homolog doesn’t affect that of another
  • Assumes every gene is found (or behave like they are) on different chromosomes and are not inherited together

                    Describes alleles of different genes