The individual genotypes in a breeding population, taken as a whole, are the

The individual genotypes in a breeding population, taken as a whole, are the gene pool.

A gene pool can be described as a collection of different genes(includes both genes expressed, and not expressed) within an interbreeding population. Definition of the gene pool can also be: the sum of all the alleles at all of the loci within the genes of a population of a single species.  

answer: the blood-brain barrier is a layer of specialized membranes and cell processes designed to keep undesirable substances from passing from the bloodstream into the precious tissues of the brain. while the blood-brain barrier does keep most bad things out of the central nervous system, it is not impermeable.

explanation:

most community's take hundreds of years to become stable