Once a person is adopted (either as a child or as an adult) all inheritance rights of the biological family of the decedent are terminated.
In the past, prior to the legalization of same-sex marriage, many partners in same-sex relationships adopted each other, to create a legal recognition of the relationship. Adoption also happens often during second marriages, when one biological parent has either died or abandoned the child. Adoption also frequently happens now by grandparents adopting their own grandchildren, whom they are raising full time, because the biological parents are either in jail or addicted to drugs.
When adoption happens, all past biological relationship is terminated for the purpose of inheritance.