Who provided the first experimental evidence for the polygenic concept of inheritance?

Polygenic traits exhibit $....$.

Which one of the following is an example of polygenic inheritance?

In human beings,the colour of skin is controlled by

$A$ polygenic trait is controlled by $3$ genes $A, B$,and $C$. In a cross $AaBbCc \times AaBbCc$,the phenotypic ratio of the offspring is observed as $1:6:x:20:x:6:1$. What is the possible value of $x$?

In a dihybrid cross,instead of a $9:3:3:1$ ratio,a $1:4:6:4:1$ ratio is obtained. This is an example of .....