CHAPTER 1 0Neural Development and Neuroplasticity
From the fusion of a female egg and a male sperm comes the develop-
ment of an animal body with all its grand complexity. This scenario of
one cell (the fertilized egg) becoming the trillions of intricately con-
nected and interacting cells of the adult animal has to be among the
most mind-boggling phenomena imaginable. How does this happen?
Not all that long ago this was a complete enigma. Now, after decades
of investigation, some understanding of cellular and molecular pro-
cesses involved in the orchestration of organismal development is
emerging. It begins with information contained in the genes, encoded
in the DNA of the body’s cells.
Every cell in the human body contains the same genetic material.
The human genome consists of forty-six chromosomes: twenty-
three inherited from the mother and twenty-three inherited from
the father. Chromosomes from the two parents carry similar infor-
mation—the same genes, although there are often different variants
of some of the genes between the parents. The two sex chromosomes
—an X from the mother and either an X or a Y from the father—have
more differences between them, because they are responsible for sex-
specific aspects of structure and function. For humans, twenty-three