Which of the following statement not describe the concept of morphogenetic gradient?

Three genes involved in determining the proximal-distal axis of the drosophila’s leg. In the third instar leg disc, the center of the disc secretes the highest concentration of two paracrine factors Wingless and Decapentaplegic. High concentrations of these paracrine factors induce expression of the Distal-less gene. Moderate concentrations induce the expression of the dachshund gene, and lower concentrations induce the expression of the homothorax gene.

Once inside the oocyte, bicoid mRNA attaches to dynein proteins that are maintained at the microtubule organizing center (the slower growing “minus end”) at the anterior of the oocyte. About 90% of the bicoid mRNA is localized to the anterior 20% of the embryo, with its concentration peaking at 7% egg length.

In the anterior region, Bicoid protein prevents translation of the caudal message to specify head and thorax structures, while in the posterior region, nanos protein prevents translation of the hunchback message to specify abdomen.

In the frog Xenopus laevis the specification of different mesodermal cell types by activin. At high concentrations, activin induced expression of the goosecoid gene to specify dorsal most structures, at slightly lower concentrations of activin the same tissue activated the Xbra gene and was specified to become muscle. At still lower concentrations, these genes were not activated, and the “default” gene expression instructed the cells to become blood vessels and heart.