Can an O neg mother and B father have child?

Yes, an O neg mother can have children with a B father. The possible blood types of the children would be:

- B Rh-negative: This is the most common blood type for children of O neg mothers and B fathers.

- B Rh-positive: This is possible if the father is Rh-positive and the mother carries an Rh-positive gene from one of her parents.

- A Rh-negative: This is possible if the father carries and passes an A allele to the child, and the mother carries an O allele and an A allele from one of her parents.

- A Rh-positive: This is possible if the father is Rh-positive and the mother carries and A allele and an Rh-positive gene from one of her parents.

The blood type of the child will depend on the specific genes inherited from each parent.