Qualitative traits are usually
Qualitative traits exhibit discontinuous phenotypic distribution with clearly separable classes such as purple versus white flowers, round versus wrinkled seeds or presence versus absence of band. They are usually monogenic or oligogenic, controlled by one or few major genes showing Mendelian ratios and limited environmental sensitivity. Variation is discrete, individuals classified unambiguously, contrasting with quantitative continuous traits like height governed by many genes. Such monogenic discontinuous nature allows simple pedigree and linkage mapping interpretation in teaching. Mastery
Ref: Falconer & Mackay, Introduction to Quantitative Genetics, 4th ed., Chapter 1: Qualitative Traits