It is because the males are heterozygous in terms of sex chromosome. They carry one copy of the X chromosome and one copy of the Y chromosome. So, only a single copy of allele is enough to produce the phenotype.
Your fill in the blank answer is: Homeostasis
Answer:
The brain and the spinal cord are wrapped in three protective layers of tissue called the meninges. The cerebral spinal fluid goes between these layers to provide more cushion and protection. It nourishes and protects the nerve tissues of the brain and spinal cord. It also acts as a shock absorber, considering humans move a lot and fall.
The answer is, "It has membrane-bound organelles."