In determining whether a bird's feet will be webbed, inhibits the expression of

In determining whether a bird's feet will be webbed, Gremlin
inhibits the expression of BMP4

BMP4 is Bone morphogentic protein 4 which is found in the chromosome and takes part in the superfamily of transformation growth factor-beta.
BMP4 is involved in the development of the cartilages and the bones and is extremely important in the onset of endochondral bone formation.

6, 4, 5, 1 are true. the others are false.