What do the letters on the inside of the puunnett squre stand for

The possible genotypes of their children

Explanation:

A punnet square can be described as a diagram which  illustrates the outcomes of a cross. The letters on the outside of a punnet square depict the genotype of the parents whereas the letters on the inside depict the genotype of the children.

For example consider the following punnet square:

        A          a

A    AA       Aa

a     Aa      aa

In the following punnet square, Aa and Aa are the genotypes of the parents.

the children would have the probability of having the following genotypes: AA, Aa, Aa, aa

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: