23andMe’s African Genetics Project is offering kits at no cost to people with all four of their grandparents born in the same African country or from the same ethnic or tribal group within one of the following countries — Angola, Benin, Burkina Faso, Cameroon, Ethiopia, Gabon, Gambia, Guinea Bissau, Guinea, Ivory coast, Liberia, Republic of Congo, Senegal, Somalia, Sudan and Togo. These countries are a priority for 23andMe because the majority of slaves brought from Africa to the Americas were brought from these African locations.
https://blog.23andme.com/23andme-research/the-african-genetics-project/