Which trait in humans exhibits polygenic 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 $x$?

Human skin color is determined by polygenic inheritance. How many types of phenotypes will be produced by the cross $AaBbCc \times AaBbCc$?

Human skin colour is an example of

In tomatoes,a plant with the genotype $aabbcc$ produces $100 \,g$ tomatoes,and a plant with the genotype $AABBCC$ produces $160 \,g$ tomatoes. What is the contribution of each polygene to the tomato weight (in $,g$)?

It is easier to study polygenic inheritance of characters in plants than in animals because in plants: