The correct answer is p53 gene.
This is one of the most important genes in our bodies, which is evident by its nickname of the "guardian angel of the genome." It is called that way because it protects our cells from becoming cancerous. It also activates many other genes.
The principle is called CEPHALOCAUDAL PRINCIPLE.
This principle proposed that growth follow a particular pattern in which the head and the upper part of the body grow first before the growth proceeds to other part of the body.
It was from nuclear fusion. (Sorry if it’s wrong but I’m pretty sure it’s not!)
Leukopenia means a low count of white blood cells in the body. When there is a low white blood cell count in the body, and in particular a low level of neutrophils (a kind of white blood cell that fights infection), there is quite a significant risk of developing an infection, and once an infection is developed and the white blood cell count is low, the body will not be able to protect itself and fight off the infection. In severe cases , infection may lead to death.