Can a rh- and an make O baby?

No, a Rh− and an O− cannot make an O− baby.

The Rh factor is a protein that is found on the surface of red blood cells. People who have the Rh factor are Rh-positive, while those who do not have the Rh factor are Rh-negative. The O blood type is a blood group that is characterized by the absence of the A and B antigens on the surface of red blood cells.

A person's blood type is determined by the genes they inherit from their parents. There are three different Rh genes: C, c, and E. A person who is Rh-positive must have at least one C or E gene, while a person who is Rh-negative must have two c genes.

A person who is O− must have two o genes, which code for the absence of the A and B antigens.

If an Rh− person and an O− person have a child, the child can only be O−. This is because the Rh− parent can only pass on a c gene, and the O− parent can only pass on an o gene. Therefore, the child will have two c genes and two o genes, which will result in an O− blood type.