8.1 The Origins of Genetics

Mendel and Others Studied Garden-Pea Traits

A. Genetics is the study of heredity, which is the passing of traits from parents to offspring

     1. Mendel was successful in determing the basic laws of heredity 
     because of his experimental method

     2. Mendel`s approach was mathematical, using many repeated trials to      
     find the likely outcome from a large sample size

     3. Mendel choose to study garden peas, Pisum sativa, which has 
     many useful features

          a. many traits with 2 distinct forms (no intermediates)
          b. mating can be controlled, using either self-fertilization or cross-
          fertilization
          c. small, grows easily, matures quickly, produces many offspring

B. Mendel oberseved that traits are expressed in simple ratios

     1. Monohybrid crosses involve one pair of contrasting traits

          a. Step 1: use self-fertilization for several generations to ensure that 
          parental generations are true-breeding
          b. Step 2: cross-fertilize two contrasting P generation plants, with 
          offspring known as the F1 generation (1st filial generation)
          c. Step 3: allow F1 generation to self-fertilize, producing the
          F2 generation (2nd filial generation)
     2. Mendel`s results
          a. F1 generation always shows one of the two contrasting traits,
          known as the dominant trait (recessive not seen) 
          b. F2 generation always shows both traits, but in a 3:1 ratio of
          dominant to recessive
          c. 3:1 ratio of dominant:recessive was constant for seven different
          pairs of contrasting traits studied by Mendel

8.2 Lecture Notes