Which characteristic is responsible for human skin color?

In human beings,multiple genes are involved in the inheritance of

Inheritance of skin color in humans is an example of which of the following?

The grain color in wheat is controlled by three pairs of polygenes. When a red-grained wheat variety is crossed with a white-grained variety,an $F_1$ hybrid is produced. When the $F_1$ hybrid is self-pollinated,what fraction of the $F_2$ generation will resemble the parental phenotypes?

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

Who first noted polygenic inheritance?