Topic 5 Quantitative genetics

1. Discontinuous vs. continuous variation
   A. Discontinuous variation = qualitative differences, almost everything we have talked about so far
       1) There are two or more clear-cut alternatives for the trait
       2) Examples, tall vs. dwarf, red vs. white
   B. Continuous variation = qualitative differences
       1) There are no clear-cut alternatives, many factors collectively determine the trait
       2) Examples, height or IQ in humans, yield or stalk strength in plants
   
   
2. Traits that show continuous variation are characterized by two criteria:
   A. They are controlled by more than one pair of alleles in an additive way
   B. They are often highly influenced by the environment
   
   
3. Quantitative inheritance = polygenic inheritance
   A. Example 1, wheat kernel color (controlled by 2 loci)
   B. Example 2, height in plants (controlled by 3 loci)
   C. Generalizations
   D. Corolla length in tobacco
   E. In examples 1 and 2 above, we have made the following assumptions:
       1). Each locus contributes equally to the trait
       2) No dominance occurred
       3) We did not consider the impact of the environment
   F. In actual quantitative inheritance studies,
       1) Different loci have different impacts on the trait
       2) Dominance is frequently involved
       3) Quantitative traits are greatly impacted by the environment

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Updated 9/25/00