A man with the autosomal recessive disorder phenylketonuria (PKU) and a woman without PKu heve a son named Peter, who does not have PKU. Peter is curious about whether hs mother is a carrier for PKiu Which fact would allow him to know Peter's matemal grandmother does not have PkU.
1. Peter's maternal grandfather does not have PkU
2. Peters maternal grandfather has PKu
3. Peter submits his own blood semple to a local genotyping lab, which establishes that he is a carrier for Pku
4. Peter's own daughter has PKU

2. Peter's maternal grandfather has PKU.

Explanation:

Such type of the genetic disorder in which two copies of a gene must be mutated at a time is called autosomal recessive disorder such as sickle cell anemia, phenylketonuria, and some other diseases. When a sing copy of a gene is mutated in a person then this disorder is not appeared and the person is called a carrier.  So when a child is born by two carrier parents then there is a chance that a child will be affected if both the parents donate mutated genes. In the case of Peter, since peter does not show this defect this means his maternal grandfather was affected by this disorder.