Traditionally, traits are divided into two categories: 1) qualitative or Mendelian traits, and 2) quantitative traits. Qualitative traits are those traits controlled by one or two (and rarely a few) genes, none of which is signifi cantly infl uenced by the environment. The effect of each gene is typically “large” and discernable in nature and overall, will result in discrete, observable, phenotypic classes. For qualitative traits, the individual’s phenotype is usually a clear representation of its genotype. These traits are also referred to as simply inherited traits and the genetic discipline that focuses on these traits is known as Mendelian genetics. Traits such as seed color, seed shape, pod shape, pod color and petal color observed by Gregor Mendel among pea plants are good examples of such traits. These traits enabled Mendel to formulate the two basic laws of genetics: the law of segregation and the law of independent assortment. These two laws, formulated between 1856 and 1863, are still fundamental in predicting the mode of genetic inheritance of traits.