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

$A$ 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 $x$?

Inheritance of skin colour in humans is an example of

What color will a gene present in a recessive homozygous condition impart to the skin in polygenic inheritance?

Grain colour in wheat is determined by three pairs of polygenes. Following the cross $AABBCC$ (dark colour) $\times$ $aabbcc$ (light colour),in $F_2$ generation,what proportion of the progeny is likely to resemble either parent?

The kernel color of wheat is determined by three pairs of polygenes. In a cross between $AABBCC$ (dark color) and $aabbcc$ (light color),what will be the proportion of $F_2$ progeny having a kernel color similar to either of the two parents?