Tbx4 and Tbx5 are critical in the specification of hindlimbs and forelimbs, respectively. The following statements describe experiments involving their expression of Tbx4 or Tbx5 genes and their probable outcomes:
A. When chick embryo was made to express Tbx4 throughout the flank tissue, limbs induced in the anterior region often become legs instead of wings.
B. Loss of Tbx4 function in the hindlimb field completely inhibits leg initiation and growth.
C. Loss of Tbx5 gene in chick results in complete failure of forelimb formation which including even the most proximal shoulder/girdle structure.

Which one of the following options represents all correct statements as made above?

Correct option is D

Explanation-

Statement A -"When chick embryo was made to express Tbx4 throughout the flank tissue, limbs induced in the anterior region often become legs instead of wings." -  CORRECT
This is a classic experiment. Forced expression of Tbx4 in regions where wings should form reprograms the identity of those limbs. Instead of forming wings (forelimbs), the chick forms legs (hindlimbs). This shows that Tbx4 is sufficient to induce hindlimb identity.

Statement B - "Loss of Tbx4 function in the hindlimb field completely inhibits leg initiation and growth."  -  CORRECT
Tbx4 is necessary for hindlimb development. When Tbx4 is knocked out or silenced in chicks or mice, hindlimbs do not form or are severely underdeveloped. This proves that Tbx4 is essential for both initiation and growth of hindlimbs.

Statement C - "Loss of Tbx5 gene in chick results in complete failure of forelimb formation which includes even the most proximal shoulder/girdle structure."  - CORRECT
 Tbx5 is critical for forelimb initiation. When Tbx5 is deleted or blocked in embryos, no forelimb forms at all, not even the proximal components like the shoulder. This demonstrates Tbx5's essential role even in the earliest steps of forelimb formation.

So, the correct answer is option d - A , B and C