Major Differences Between qualitative and quantitative inheritance

Qualitative Inheritance

1. Characters of Kind

2. Discontinuous variation

3. Single gene effects visible

4. Analysis is rather simple

Quantitative Inheritance

1. Characters of Degree

2. Continuous variation

3. Single gene effects not seen

4. Analysis needs appropriate satistical method and mostly complicated.

Multiple gene model, developed by the Swedish geneticis Xilsson-Ehle in 1910 to explain inheritance of kernel colour in wheat is treated as a classical example of a bridge between the two types of inheritance pattern.

When he crossed a red strain to a white strain, he observed that F_i plants had light red wheat and in F₂ approximately 1/16 were red and 1/16 were white and the others showed a gradation from one extreme to the other. He interpreted these results in terms of two genes but each with a pair of alleles exhibiting cumulative effects.

(Red) (Medium) (Light Red) (Very Light) (White)

The presumption is that, each of the RI or R2 (dominant) adds to the redness of the kernel in the phenotypes so that the phenotype with neither of these alleles turned out to be white. The F 2 distribution is an expression of (a+b)4 where a =b=¹/.₎

These multiple gene models help us understand the origin of continuous variation characterizing truly quantitative traits. Hut, it should be remembered that environment docs modify the phenotypes to different degrees in different systems. So, it is important to discount the environmental effects from the observed inheritance pattern to assess if heritability of quantitative trait is high. These findings help plant breeders in their selection methods.