Why is it that some people can consume lactose and others are considered lactose intolerant?

John and jane jones’ newborn baby girl, leah, has just been diagnosed with galactosemia. prior to their genetic counseling appointment, they submitted this family history: john and jane’s older child, a son named lee, does not have galactosemia. john is the only child of hanna and harry. harry was an only child. hanna has two older sisters, hope (the oldest) and holly. both harry and hanna’s parents lived in good health into their 80s. jane’s brother, joe, is married to jen. they have a son, les, who is a healthy nine-year-old with myopia (nearsightedness) but no sign of galactosemia. jane’s mother, hilda, is alive and healthy; jane’s father, henry, passed away last year of a sudden heart attack. hilda and henry have no family history of galactosemia. use the information in the family history to construct a pedigree for this family.