How does a majority of a people with 20 percent or so of an ancestry manifest a specific physical trait?

Specifically, Africans. 99 percent of all Africans have no facial or body hair, whereas basically the whole majority of their American counterpart (African Americans) can grow facial hair with only 20 percent or so of European blood. What are the chances of displaying a specific trait in a majority of a people who... show more Specifically, Africans. 99 percent of all Africans have no facial or body hair, whereas basically the whole majority of their American counterpart (African Americans) can grow facial hair with only 20 percent or so of European blood.

What are the chances of displaying a specific trait in a majority of a people who have just around one fourth of a certain ancestry group?

Serious question. If you have something to say that is unrelated to this post, please don't leave a comment.
Update: This is a biological question. It is not an anthropological or archaeological question so I ask you to please not move this.
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