Predict how the milk digestion is affected in individuals that lack functional copies of the gene encoding lactase. Justify your response.

Such individuals will be unable to digest milk.

Explanation:

Milk is a substance that contains a disaccharide sugar called LACTOSE. Lactose is a disaccharide sugar composed of glucose and galactose monomers. In order to digest the lactose sugar present in milk, an enzyme called LACTASE is needed.

Since lactase, like every other enzyme, is a protein, it is coded for by a functional gene. However, in an individual that lack functional copies of the gene encoding this lactase enzyme (protein), such individual will be unable to synthesize lactase, hence, be unable to breakdown (digest) lactose sugar in milk.

No lactase gene -> No lactase protein -> No enzyme -> No milk digestion