Final answer:
The ability to digest lactose is primarily dependent on the enzyme lactase. Lactose intolerance is a condition where individuals lack or have a deficiency of lactase, making them unable to digest lactose.
Step-by-step explanation:
The ability or non-ability to digest lactose, a sugar found in milk, is primarily dependent on the enzyme lactase. Lactase is responsible for breaking down lactose into smaller, more easily digestible sugars. Individuals who lack or have a deficiency of lactase are unable to digest lactose and are therefore considered lactose intolerant. This condition is primarily influenced by genetic factors.