Question

every human cell contains the gene that codes for a milk protein called casein. however, the gene is expressed only in lactating females. what causes the limited expression of this gene?

the gene for production of casein is not activated in other human cells

the gene for production of casein is active only in newly formed cells

the gene for production of casein is lost due to repeated cell division

the gene for production of casein is mutated in other human cells

Explanation:

Gene expression is regulated. In this case, the gene for casein production is present in all human cells (so it's not lost or mutated in non - lactating cells). Newly formed cells aren't the relevant factor here. The key is that in non - lactating cells, the gene for casein production is not activated.

Answer:

The gene for production of casein is not activated in other human cells.