Mendel's Hypotheses

Methods of research

  • choose Garden Peas
    . . - had available several varieties
    . . - could control breeding
  • started with "pure bred" [homozygous] or true-breeding plants,
    . . - P-1 = parental generation
  • produced "hybrid" [heterozygous] offspring to compare traits to parents,
    . . - F-1 = first filial generation
  • crossed hybrid to hybrid offspring to follow trait further,
    . . - F-2 = second filial generation [inbred]
    . . - F-n = nth filial generation [inbred]
    Mendel's hypotheses
  • Each organism receives one allele for each trait from each parent
  • [therefore] all organisms must have two alleles for each trait
  • Alleles segregate independently during gamete formation
  • Alleles are paired by fertilization, a random pairing of gametes
  • (Some) traits exhibit "dominance"
    . . - heterozygote resembles one of homozygotes

    Independent segregation in di-hybrid, tri-hybrid, etc.

  • Gamete formation in monohybrid
    AA A A
    Aa A a
    aa a a

  • Gamete formation in dihybrid
    AA BB A B A B A B A B
    AA Bb A B A b A B A b
    AA bb A b A b A b A b
    Aa BB A B A B a B a B
    Aa Bb A B A b a B a b
    Aa bb A b A b a b a b
    aa BB a B a B a B a B
    aa Bb a B a b a B a b
    aa bb a b a b a b a b

    © 2004 Prof. LaFrance, Ancilla College