The correct answer is (2) lactoglobulin and casein.

Why lactoglobulin and casein promoters are used

• In transgenic dairy cattle, the goal is to express human therapeutic proteins specifically in the mammary gland and secrete them into milk.

• Promoters from major milk protein genes (e.g., β‑lactoglobulin and caseins) are:

  • Strongly active during lactation.

  • Mammary gland–specific, minimizing ectopic expression.

  • Well-characterized and successfully used to drive high-level expression of pharmaceuticals like human α‑lactalbumin, antithrombin, and others in cow, goat, and sheep milk.

Thus, lactoglobulin and casein promoters fit the requirement best.

Why the other options are less appropriate

• (1) Lactalbumin and ovalbumin

  • α‑Lactalbumin is a milk protein, but ovalbumin is the major egg-white protein of birds, not a bovine milk protein.

  • Ovalbumin promoter is used in transgenic poultry (e.g., expressing proteins in egg white), not in dairy cattle.

• (3) Lactoferrin and transferrin

  • Lactoferrin is present in milk but at lower levels and is not the standard high-output promoter of choice.

  • Transferrin is a serum iron‑binding protein; its promoter is not mammary‑specific and is not commonly used for milk-based expression.

• (4) Casein and ovalbumin

  • Casein is appropriate, but ovalbumin again is an egg protein promoter, not typically used in cows.

Therefore, the pair of promoters “extensively used for production of pharmaceutical proteins in transgenic dairy cattles” is lactoglobulin and casein (option 2).