Law of segregation.
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   Each plant inherits 1 allele for flower color from each parent.
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   The  2  alleles  segregate  (separate) and end up in different gametes
   during meiosis.
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   Random   fertilization   yields   predictable  offspring  ratios:  3:1
   phenotypic ratio, 1:2:1 genotypic ratio.
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   These ratios can be modeled by a Punnett square: list all the possible
   female  gametes along one side and all the possible male gametes along
   the other side, then combine the gametes to produce offspring.